feat(webui): vue admin panel source

Vue 3 + TypeScript + Pinia + Tailwind v4 + shadcn-vue + Chart.js admin
panel source under webui/, built with Vite. Views: Overview (providers,
redis/cache/retry status, model aliases), Usage (per-user/per-group/total
tables with tokensIn/tokensOut/cost + limits), Charts (scope selector,
req/tokens(stacked in-out)/cost metric tabs, 24h/30d/12mo window
switcher, fed by GET /admin/api/usage/history). Pinia stores: auth
(sessionStorage key gate, x-api-key header, 401/403 re-prompt),
dashboard (5s poll), history (fetch-on-selection + 30s refresh).

Design: deliberate neutral warm-neutral palette with a signature teal
accent (no default Inter/purple-gradient/glassmorphism), real
typographic hierarchy via the platform UI/mono font stacks (zero
external assets - no Google Fonts), dark+light via prefers-color-scheme
(no class toggle, no theme switcher). Charts: zero-based bars, honest
axes, Okabe-Ito colorblind-safe series, tokens-in/out as a
distinguishable stacked pair.

vite.config.ts: base '/admin/' (matches admin.go's route layout) and
build.modulePreload.polyfill:false (no inline bootstrap script, so the
tightened admin CSP needs no 'unsafe-inline'). Code-split: Chart.js
(ChartsView) loads lazily, not in the initial bundle.

generate.mjs reads dist/ after `vite build` and writes
../admin_assets_gen.go (not committed by this change) - base64-encodes
every asset, decoded once at package-var init; documented rationale in
the script's own header comment.

Hygiene: webui/go.mod walls webui/ off from the repo root's `go build`/
`vet`/`test ./...` (npm's node_modules bundles a stray .go file that
would otherwise be swept in); tools/yaegi-check/main.go excludes webui/
from its GOPATH copy for the same reason. webui/ export-ignored
(.gitattributes) from release source tarballs; webui/node_modules/
gitignored. tsconfig.app.json/tsconfig.node.json's JSONC comments
dropped (TS itself is fine with either; the global pre-commit JSON
validator is not) - no config values changed.

webui/package.json

@@ -0,0 +1,37 @@
+{
+  "name": "webui",
+  "private": true,
+  "version": "0.0.0",
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "vue-tsc -b && vite build",
+    "preview": "vite preview"
+  },
+  "dependencies": {
+    "@fortawesome/fontawesome-svg-core": "^7.3.1",
+    "@fortawesome/free-solid-svg-icons": "^7.3.1",
+    "@fortawesome/vue-fontawesome": "^3.3.3",
+    "@vueuse/core": "^14.4.0",
+    "chart.js": "^4.5.1",
+    "class-variance-authority": "^0.7.1",
+    "clsx": "^2.1.1",
+    "pinia": "^4.0.3",
+    "reka-ui": "^2.10.3",
+    "shadcn-vue": "^2.8.2",
+    "tailwind-merge": "^3.6.0",
+    "tw-animate-css": "^1.4.0",
+    "vue": "^3.5.40",
+    "vue-chartjs": "^5.3.4"
+  },
+  "devDependencies": {
+    "@tailwindcss/vite": "^4.3.3",
+    "@types/node": "^24.13.3",
+    "@vitejs/plugin-vue": "^6.0.8",
+    "@vue/tsconfig": "^0.9.1",
+    "tailwindcss": "^4.3.3",
+    "typescript": "~6.0.2",
+    "vite": "^8.2.0",
+    "vue-tsc": "^3.3.8"
+  }
+}