fix: auth login flow, Next.js 16 upgrade, ESM/CJS compatibility

- Upgrade Next.js 15 → 16.1 and rename middleware.ts → proxy.ts
- Fix ESM/CJS compatibility: remove "type": "module" from config/shared packages, switch to commonjs
- Fix Better Auth integration: text IDs for sessions/accounts/verifications, wildcard route @All("**"), proper password hash for admin seed
- Fix auth-client to use window.location.origin instead of hardcoded localhost:4000
- Fix api-client, forgot-password, reset-password to use relative /api/ URLs (via Next.js proxy)
- Fix TimeoutInterceptor DI by using useValue instead of useClass
- Add Playwright E2E login tests for localhost and v2.sase.tr
- Add missing UI components: vin-input, vehicle-card, category-tree

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

apps/web/package.json

@@ -19,7 +19,7 @@
     "better-auth": "^1.2.0",
     "clsx": "^2.1.0",
     "lucide-react": "^0.468.0",
-    "next": "^15.1.0",
+    "next": "^16.1.0",
     "react": "^19.0.0",
     "react-dom": "^19.0.0",
     "sonner": "^1.7.0",
@@ -28,6 +28,7 @@
     "zustand": "^5.0.0"
   },
   "devDependencies": {
+    "@playwright/test": "^1.58.2",
     "@tailwindcss/postcss": "^4.0.0",
     "@testing-library/jest-dom": "^6.9.1",
     "@testing-library/react": "^16.3.2",