feat(browser-ext): move browser extension to browser-ext/ and update API client to tRPC

- Create browser-ext/ with full extension code (MV3 manifest, background
  service worker, content script, popup, options page)
- Add tRPC API client that communicates with unified monolith endpoints
- Implement cache, settings, and phishing detection utilities
- Create extension tRPC router in web app (getAuthStatus, linkDevice,
  reportPhishing)
- Configure Vite build with manifest V3 support
- Write unit tests for cache, phishing detector, and API client
- All 20 tests passing, TypeScript lint clean

browser-ext/package.json

@@ -1,10 +1,26 @@
 {
-  "name": "browser-ext",
+  "name": "@shieldai/browser-ext",
   "version": "0.1.0",
   "private": true,
+  "type": "module",
   "scripts": {
-    "build": "echo 'browser-ext build placeholder'",
-    "dev": "echo 'browser-ext dev placeholder'",
-    "test": "echo 'browser-ext test placeholder'"
+    "dev": "vite build --watch",
+    "build": "vite build",
+    "build:chrome": "vite build --mode chrome",
+    "build:firefox": "vite build --mode firefox",
+    "test": "vitest run",
+    "test:watch": "vitest",
+    "lint": "tsc --noEmit"
+  },
+  "dependencies": {
+    "@trpc/client": "^10.45.2",
+    "@trpc/server": "^10.45.2",
+    "superjson": "^2.2.1"
+  },
+  "devDependencies": {
+    "@types/chrome": "^0.0.280",
+    "typescript": "^5.7.0",
+    "vite": "^6.0.0",
+    "vitest": "^4.1.5"
   }
 }