ci: build Windows binaries; add cross-platform CI test matrix

- release.yml: add x86_64-pc-windows-msvc target, OS-aware packaging (.exe + .zip)
- ci.yml: split into lint (fmt/clippy) + test matrix (ubuntu/windows/macos)
- use getrandom for the admin/key token CSPRNG (secure on Windows too)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -2,11 +2,11 @@ name: CI
 
 on:
   push:
-    branches: [ main, master ]
+    branches: [main, master]
   pull_request:
 
 jobs:
-  build:
+  lint:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
@@ -18,6 +18,18 @@ jobs:
         run: cargo fmt --all -- --check
       - name: Clippy
         run: cargo clippy --all-targets -- -D warnings
+
+  test:
+    name: test (${{ matrix.os }})
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, windows-latest, macos-14]
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+      - uses: Swatinem/rust-cache@v2
       - name: Build
         run: cargo build --release
       - name: Test