feat(ui): F0 — Tailwind + design tokens + theme infrastructure

Install Tailwind v3, Radix primitives, cva/tailwind-merge/clsx, lucide-react.
Add HSL design tokens (light + dark) with the Indigo #5b5bf0 accent isolated
to a single --primary token (swappable for a future accent picker), darkMode
'class', anti-flash inline script, useTheme hook, and cn() helper. styles.css
still loads for not-yet-migrated pages. Build green.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/package.json

@@ -9,16 +9,35 @@
     "preview": "vite preview --host"
   },
   "dependencies": {
+    "@radix-ui/react-avatar": "^1.2.1",
+    "@radix-ui/react-checkbox": "^1.3.6",
+    "@radix-ui/react-dialog": "^1.1.18",
+    "@radix-ui/react-dropdown-menu": "^2.1.19",
+    "@radix-ui/react-label": "^2.1.11",
+    "@radix-ui/react-popover": "^1.1.18",
+    "@radix-ui/react-scroll-area": "^1.2.13",
+    "@radix-ui/react-separator": "^1.1.11",
+    "@radix-ui/react-switch": "^1.3.2",
+    "@radix-ui/react-tabs": "^1.1.16",
+    "@radix-ui/react-toast": "^1.2.18",
+    "@radix-ui/react-tooltip": "^1.2.11",
     "axios": "^1.7.2",
     "chart.js": "^4.4.3",
+    "class-variance-authority": "^0.7.1",
+    "clsx": "^2.1.1",
+    "lucide-react": "^1.22.0",
     "react": "^18.3.1",
     "react-chartjs-2": "^5.2.0",
     "react-dom": "^18.3.1",
     "react-grid-layout": "^1.4.4",
-    "react-router-dom": "^6.24.0"
+    "react-router-dom": "^6.24.0",
+    "tailwind-merge": "^3.6.0"
   },
   "devDependencies": {
     "@vitejs/plugin-react": "^4.3.1",
+    "autoprefixer": "^10.5.2",
+    "postcss": "^8.5.16",
+    "tailwindcss": "^3.4.19",
     "vite": "^5.3.1"
   }
 }