feat(frontend): Implement complete authentication system

Implemented comprehensive JWT-based authentication with token refresh mechanism, user state management, and protected routes.

Changes:
- Upgraded API client from fetch to Axios with automatic token refresh interceptors
- Created API configuration with centralized endpoint definitions
- Implemented Zustand auth store for user state management with persistence
- Created React Query hooks for login, register, logout, and current user
- Built login and registration pages with form validation (Zod + React Hook Form)
- Implemented AuthGuard component for route protection
- Enhanced Header with user dropdown menu and logout functionality
- Updated Sidebar with user information display at bottom
- Added Team navigation item to sidebar
- Configured environment variables for API base URL

Technical Details:
- JWT token storage in localStorage with secure key names
- Automatic token refresh on 401 responses
- Request queueing during token refresh to prevent race conditions
- TypeScript strict typing throughout
- ESLint compliant code (fixed type safety issues)
- Proper error handling with user-friendly messages

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

package.json

@@ -17,6 +17,7 @@
     "@radix-ui/react-slot": "^1.2.3",
     "@tanstack/react-query": "^5.90.6",
     "@tanstack/react-query-devtools": "^5.90.2",
+    "axios": "^1.13.1",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
     "lucide-react": "^0.552.0",