feat(frontend): scaffold Vite+React+TS+Tailwind/ShadCn + Vitest

TDD: App-renders-ThothII test RED then GREEN. ShadCn v4 (base-nova style)
init + button/checkbox/radio-group/textarea/card/dialog/badge/sonner added.
tailwind.config.ts extended with oklch CSS-variable color mapping required
by ShadCn v4 @apply directives. npm test passes; npm run build clean.

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

frontend/tsconfig.json

@@ -0,0 +1,19 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "useDefineForClassFields": true,
+    "lib": ["ES2022", "DOM", "DOM.Iterable"],
+    "module": "ESNext",
+    "moduleResolution": "Bundler",
+    "jsx": "react-jsx",
+    "strict": true,
+    "noEmit": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "types": ["vitest/globals", "@testing-library/jest-dom"],
+    "paths": {
+      "@/*": ["./src/*"]
+    }
+  },
+  "include": ["src"]
+}