Add shadcn/ui design system, theme, and base components

Install shadcn/ui with base-nova style, tailwind-merge, tw-animate-css,
and font packages. Add oklch-based light/dark theme in index.css and
17 base UI components (button, card, dialog, table, tabs, etc.) plus
shared lib utilities (format, colors, cn) and useSettings hook.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/package.json

@@ -9,12 +9,21 @@
     "preview": "vite preview"
   },
   "dependencies": {
+    "@base-ui/react": "^1.3.0",
+    "@fontsource-variable/ibm-plex-sans": "^5.2.8",
+    "@fontsource-variable/noto-sans": "^5.2.10",
+    "@tanstack/react-table": "^8.21.3",
     "axios": "^1.13.6",
+    "class-variance-authority": "^0.7.1",
+    "clsx": "^2.1.1",
     "lucide-react": "^0.562.0",
     "react": "^19.2.0",
     "react-dom": "^19.2.0",
     "react-router-dom": "^7.12.0",
-    "recharts": "^3.8.0"
+    "recharts": "^2.15.4",
+    "shadcn": "^4.1.0",
+    "tailwind-merge": "^3.5.0",
+    "tw-animate-css": "^1.4.0"
   },
   "devDependencies": {
     "@tailwindcss/vite": "^4.1.18",