feat: add admin dashboard, audit logs, token expiry check and test suite

Frontend Features:
- Add ProtectedRoute component with token expiry validation
- Create AdminDashboardPage with system statistics and user management
- Create AuditLogsPage with filtering and pagination
- Add admin-only navigation (Shield icon) for ymirliu@panjit.com.tw
- Add admin API methods to apiV2 service
- Add admin type definitions (SystemStats, AuditLog, etc.)

Token Management:
- Auto-redirect to login on token expiry
- Check authentication on route change
- Show loading state during auth check
- Admin privilege verification

Backend Testing:
- Add pytest configuration (pytest.ini)
- Create test fixtures (conftest.py)
- Add unit tests for auth, tasks, and admin endpoints
- Add integration tests for complete workflows
- Test user isolation and admin access control

Documentation:
- Add TESTING.md with comprehensive testing guide
- Include test running instructions
- Document fixtures and best practices

Routes:
- /admin - Admin dashboard (admin only)
- /admin/audit-logs - Audit logs viewer (admin only)

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

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

frontend/src/types/apiV2.ts

@@ -115,3 +115,72 @@ export interface TaskFilters {
   order_by: string
   order_desc: boolean
 }
+
+// ==================== Admin Types ====================
+
+export interface SystemStats {
+  total_users: number
+  active_users: number
+  total_tasks: number
+  total_sessions: number
+  recent_activity_count: number
+  task_stats: {
+    pending: number
+    processing: number
+    completed: number
+    failed: number
+  }
+}
+
+export interface UserWithStats {
+  id: number
+  email: string
+  display_name: string | null
+  created_at: string
+  last_login: string | null
+  is_active: boolean
+  task_count: number
+  completed_tasks: number
+  failed_tasks: number
+}
+
+export interface TopUser {
+  user_id: number
+  email: string
+  display_name: string | null
+  task_count: number
+  completed_tasks: number
+}
+
+export interface AuditLog {
+  id: number
+  user_id: number
+  user_email: string
+  category: 'auth' | 'task' | 'file' | 'admin' | 'system'
+  action: string
+  resource_type: string | null
+  resource_id: string | null
+  success: boolean
+  error_message: string | null
+  extra_data: string | null
+  created_at: string
+}
+
+export interface AuditLogListResponse {
+  logs: AuditLog[]
+  total: number
+  page: number
+  page_size: number
+  has_more: boolean
+}
+
+export interface UserActivitySummary {
+  user_id: number
+  email: string
+  display_name: string | null
+  total_actions: number
+  successful_actions: number
+  failed_actions: number
+  categories: Record<string, number>
+  recent_actions: AuditLog[]
+}