fix(ui): install-command chip and bands slider readable in the light theme

The chip used var(--panel-2, #23252c) — a variable that doesn't exist with
a hard dark fallback, so in the light theme the install command was a dark
box with dark text. Same class of bug in the bands slider track and handle
labels (invented --panel-2/--fg vars). All moved to the real theme
variables (--panel/--border/--text) via a .cmd-chip class; verified by
computed styles in the light theme (text rgb(15,23,42) on white) and
screenshots of both views.

web/js/views/keys.js

@@ -270,7 +270,7 @@ console.log(resp.choices[0].message.content);`,
           h("span", { class: "muted" }, "○ " + t("keys.h.st.notFound")),
           cmd ? h("div", { class: "flex", style: "gap:6px; align-items:center; margin-top:4px" },
             h("span", { class: "muted" }, t("keys.h.install")),
-            h("code", { class: "mono small", style: "background:var(--panel-2,#23252c); padding:2px 8px; border-radius:6px" }, cmd),
+            h("code", { class: "mono small cmd-chip" }, cmd),
             copyInstall) : null);
       }
     }