feat: add dark/light theme switching with ThemeContext and localStorage persistence

frontend/src/ThemeContext.tsx

@@ -0,0 +1,46 @@
+import React, { createContext, useContext, useEffect, useState } from 'react';
+
+type Theme = 'light' | 'dark';
+
+interface ThemeContextType {
+  theme: Theme;
+  toggleTheme: () => void;
+}
+
+const ThemeContext = createContext<ThemeContextType | undefined>(undefined);
+
+export const ThemeProvider: React.FC<{ children: React.ReactNode }> = ({ children }) => {
+  const [theme, setTheme] = useState<Theme>(() => {
+    const saved = localStorage.getItem('theme');
+    if (saved === 'light' || saved === 'dark') return saved;
+    if (window.matchMedia && window.matchMedia('(prefers-color-scheme: light)').matches) {
+      return 'light';
+    }
+    return 'dark';
+  });
+
+  useEffect(() => {
+    const root = window.document.documentElement;
+    root.classList.remove('light', 'dark');
+    root.classList.add(theme);
+    localStorage.setItem('theme', theme);
+  }, [theme]);
+
+  const toggleTheme = () => {
+    setTheme(prev => (prev === 'dark' ? 'light' : 'dark'));
+  };
+
+  return (
+    <ThemeContext.Provider value={{ theme, toggleTheme }}>
+      {children}
+    </ThemeContext.Provider>
+  );
+};
+
+export const useTheme = () => {
+  const context = useContext(ThemeContext);
+  if (context === undefined) {
+    throw new Error('useTheme must be used within a ThemeProvider');
+  }
+  return context;
+};

frontend/src/components/Navbar.tsx

@@ -1,4 +1,4 @@
-import React from 'react';
+import React from 'react';
 import { 
   Activity, 
   Compass, 
@@ -6,8 +6,11 @@ import {
   Cpu, 
   BarChart3, 
   Sliders, 
-  Radio
+  Radio,
+  Sun,
+  Moon
 } from 'lucide-react';
+import { useTheme } from '../ThemeContext';
 
 interface NavbarProps {
   activeTab: string;
@@ -16,6 +19,7 @@ interface NavbarProps {
 }
 
 export const Navbar: React.FC<NavbarProps> = ({ activeTab, setActiveTab, onlineStatus = true }) => {
+  const { theme, toggleTheme } = useTheme();
   const navItems = [
     { id: 'dashboard', label: 'Control Room', icon: Activity },
     { id: 'playground', label: 'Playground', icon: Compass },
@@ -27,7 +31,7 @@ export const Navbar: React.FC<NavbarProps> = ({ activeTab, setActiveTab, onlineS
   ];
 
   return (
-    <header className="sticky top-0 z-50 w-full border-b border-[#1F2833] bg-[#07090C]/90 backdrop-blur-md">
+    <header className="sticky top-0 z-50 w-full border-b border-border-subtle bg-bg-primary/90 backdrop-blur-md">
       <div className="max-w-7xl mx-auto px-4 sm:px-6 lg:px-8 h-16 flex items-center justify-between gap-4">
         
         {/* Brand / Logo */}
@@ -35,7 +39,7 @@ export const Navbar: React.FC<NavbarProps> = ({ activeTab, setActiveTab, onlineS
           onClick={() => setActiveTab('dashboard')}
           className="flex items-center gap-3 cursor-pointer select-none shrink-0 group"
         >
-          <div className="w-10 h-10 rounded-xl bg-[#0D1117] border border-accent-primary/40 flex items-center justify-center overflow-hidden shadow-[0_0_18px_rgba(56,148,255,0.25)] group-hover:border-accent-primary transition-all p-1">
+          <div className="w-10 h-10 rounded-xl bg-bg-secondary border border-accent-primary/40 flex items-center justify-center overflow-hidden shadow-[0_0_18px_rgba(56,148,255,0.25)] group-hover:border-accent-primary transition-all p-1">
             <img 
               src="/logo.png" 
               alt="Model Router Logo" 
@@ -59,7 +63,7 @@ export const Navbar: React.FC<NavbarProps> = ({ activeTab, setActiveTab, onlineS
         </div>
 
         {/* Navigation Tabs */}
-        <nav className="hidden lg:flex items-center gap-1.5 p-1 rounded-xl bg-[#0D1117]/80 border border-[#1F2833]/80">
+        <nav className="hidden lg:flex items-center gap-1.5 p-1 rounded-xl bg-bg-secondary/80 border border-border-subtle/80">
           {navItems.map((item) => {
             const Icon = item.icon;
             const isActive = activeTab === item.id;
@@ -70,7 +74,7 @@ export const Navbar: React.FC<NavbarProps> = ({ activeTab, setActiveTab, onlineS
                 className={`flex items-center gap-2 px-3 py-1.5 rounded-lg text-xs font-mono font-semibold transition-all duration-150 whitespace-nowrap ${
                   isActive
                     ? 'bg-accent-primary text-bg-primary shadow-[0_0_12px_rgba(56,148,255,0.4)] font-bold'
-                    : 'text-text-muted hover:text-text-primary hover:bg-[#141920]'
+                    : 'text-text-muted hover:text-text-primary hover:bg-bg-card'
                 }`}
               >
                 <Icon className={`w-3.5 h-3.5 ${isActive ? 'text-bg-primary stroke-[2.5]' : 'text-text-muted stroke-[2]'}`} />
@@ -104,7 +108,15 @@ export const Navbar: React.FC<NavbarProps> = ({ activeTab, setActiveTab, onlineS
 
         {/* Status Indicator */}
         <div className="hidden sm:flex items-center gap-2 shrink-0">
-          <div className="flex items-center gap-2 px-3 py-1.5 rounded-xl bg-[#0D1117] border border-[#1F2833] font-mono text-xs shadow-inner">
+          <button 
+            onClick={toggleTheme}
+            className="p-1.5 rounded-xl bg-bg-secondary border border-border-subtle text-text-muted hover:text-text-primary hover:border-border-active transition-all"
+            title="Toggle theme"
+          >
+            {theme === 'dark' ? <Sun className="w-4 h-4" /> : <Moon className="w-4 h-4" />}
+          </button>
+          
+          <div className="flex items-center gap-2 px-3 py-1.5 rounded-xl bg-bg-secondary border border-border-subtle font-mono text-xs shadow-inner">
             <span className={`w-2 h-2 rounded-full ${onlineStatus ? 'bg-accent-success shadow-[0_0_8px_#10B981]' : 'bg-accent-error'}`} />
             <span className="text-[11px] font-bold tracking-wide text-text-primary whitespace-nowrap">
               ROUTER READY

frontend/src/index.css

@@ -1,17 +1,17 @@
-@import "tailwindcss";
+@import "tailwindcss";
 
 @theme {
-  --color-bg-primary: #07090C;
-  --color-bg-secondary: #0D1117;
-  --color-bg-card: #121820;
-  --color-bg-card-hover: #17202B;
+  --color-bg-primary: var(--theme-bg-primary);
+  --color-bg-secondary: var(--theme-bg-secondary);
+  --color-bg-card: var(--theme-bg-card);
+  --color-bg-card-hover: var(--theme-bg-card-hover);
 
-  --color-border-subtle: #1F2833;
-  --color-border-active: #324050;
+  --color-border-subtle: var(--theme-border-subtle);
+  --color-border-active: var(--theme-border-active);
 
-  --color-text-primary: #F0F4F8;
-  --color-text-muted: #8B98A5;
-  --color-text-dim: #546270;
+  --color-text-primary: var(--theme-text-primary);
+  --color-text-muted: var(--theme-text-muted);
+  --color-text-dim: var(--theme-text-dim);
 
   --color-accent-primary: #3894FF;
   --color-accent-secondary: #F59E0B;
@@ -24,19 +24,43 @@
   --font-sans: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
 }
 
+:root {
+  --theme-bg-primary: #F8FAFC;
+  --theme-bg-secondary: #F1F5F9;
+  --theme-bg-card: #FFFFFF;
+  --theme-bg-card-hover: #F8FAFC;
+  --theme-border-subtle: #E2E8F0;
+  --theme-border-active: #CBD5E1;
+  --theme-text-primary: #0F172A;
+  --theme-text-muted: #475569;
+  --theme-text-dim: #64748B;
+}
+
+.dark {
+  --theme-bg-primary: #07090C;
+  --theme-bg-secondary: #0D1117;
+  --theme-bg-card: #121820;
+  --theme-bg-card-hover: #17202B;
+  --theme-border-subtle: #1F2833;
+  --theme-border-active: #324050;
+  --theme-text-primary: #F0F4F8;
+  --theme-text-muted: #8B98A5;
+  --theme-text-dim: #546270;
+}
+
 body {
-  background-color: #07090C;
-  color: #F0F4F8;
+  background-color: var(--theme-bg-primary);
+  color: var(--theme-text-primary);
   font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
   overflow-x: hidden;
 }
 
 /* Custom glow borders and glass effects */
 .glass-panel {
-  background: rgba(18, 24, 32, 0.75);
+  background: color-mix(in srgb, var(--theme-bg-card) 75%, transparent);
   backdrop-filter: blur(12px);
   -webkit-backdrop-filter: blur(12px);
-  border: 1px solid rgba(40, 52, 68, 0.6);
+  border: 1px solid color-mix(in srgb, var(--theme-border-active) 60%, transparent);
 }
 
 .glass-panel-hover:hover {
@@ -48,8 +72,8 @@ body {
 .grid-bg {
   background-size: 28px 28px;
   background-image: 
-    linear-gradient(to right, rgba(31, 40, 51, 0.4) 1px, transparent 1px),
-    linear-gradient(to bottom, rgba(31, 40, 51, 0.4) 1px, transparent 1px);
+    linear-gradient(to right, color-mix(in srgb, var(--theme-border-subtle) 40%, transparent) 1px, transparent 1px),
+    linear-gradient(to bottom, color-mix(in srgb, var(--theme-border-subtle) 40%, transparent) 1px, transparent 1px);
 }
 
 .radar-glow {
@@ -83,12 +107,12 @@ body {
   height: 6px;
 }
 ::-webkit-scrollbar-track {
-  background: #07090C;
+  background: var(--theme-bg-primary);
 }
 ::-webkit-scrollbar-thumb {
-  background: #1F2833;
+  background: var(--theme-border-subtle);
   border-radius: 3px;
 }
 ::-webkit-scrollbar-thumb:hover {
-  background: #324050;
+  background: var(--theme-border-active);
 }

frontend/src/main.tsx

@@ -1,10 +1,13 @@
-import React from 'react'
+import React from 'react'
 import ReactDOM from 'react-dom/client'
 import App from './App'
+import { ThemeProvider } from './ThemeContext'
 import './index.css'
 
 ReactDOM.createRoot(document.getElementById('root')!).render(
   <React.StrictMode>
-    <App />
+    <ThemeProvider>
+      <App />
+    </ThemeProvider>
   </React.StrictMode>,
 )

frontend/src/pages/SettingsPage.tsx

@@ -1,8 +1,10 @@
-import React, { useEffect, useState } from 'react';
-import { Sliders, Shield, DollarSign, Cpu, CheckCircle } from 'lucide-react';
+import React, { useEffect, useState } from 'react';
+import { Sliders, Shield, DollarSign, Cpu, CheckCircle, Sun, Moon } from 'lucide-react';
 import { fetchApi } from '../lib/api';
+import { useTheme } from '../ThemeContext';
 
 export const SettingsPage: React.FC = () => {
+  const { theme, toggleTheme } = useTheme();
   const [budget, setBudget] = useState<{
     daily_limit: number;
     monthly_limit: number;
@@ -17,14 +19,24 @@ export const SettingsPage: React.FC = () => {
 
   return (
     <div className="space-y-8 max-w-4xl mx-auto pb-16 font-mono">
-      <div className="border-b border-border-subtle pb-4">
-        <h2 className="text-xl font-bold text-text-primary tracking-wide flex items-center gap-2">
-          <Sliders className="w-5 h-5 text-accent-primary" />
-          SYSTEM CONFIGURATION & BUDGET GUARDS
-        </h2>
-        <p className="text-xs text-text-muted mt-1">
-          Configure daily and monthly spend limits, routing threshold interventions, and environment parameters.
-        </p>
+      <div className="border-b border-border-subtle pb-4 flex justify-between items-start">
+        <div>
+          <h2 className="text-xl font-bold text-text-primary tracking-wide flex items-center gap-2">
+            <Sliders className="w-5 h-5 text-accent-primary" />
+            SYSTEM CONFIGURATION & BUDGET GUARDS
+          </h2>
+          <p className="text-xs text-text-muted mt-1">
+            Configure daily and monthly spend limits, routing threshold interventions, and environment parameters.
+          </p>
+        </div>
+        
+        <button 
+          onClick={toggleTheme}
+          className="flex items-center gap-2 px-3 py-1.5 rounded-lg bg-bg-secondary border border-border-subtle text-text-muted hover:text-text-primary hover:border-border-active transition-all text-xs font-bold"
+        >
+          {theme === 'dark' ? <Sun className="w-4 h-4" /> : <Moon className="w-4 h-4" />}
+          {theme === 'dark' ? 'LIGHT MODE' : 'DARK MODE'}
+        </button>
       </div>
 
       {/* Budget Management */}