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>

backend/pytest.ini

@@ -1,32 +1,13 @@
 [pytest]
-# Pytest configuration for Tool_OCR backend tests
-
-# Test discovery patterns
+testpaths = tests
 python_files = test_*.py
 python_classes = Test*
 python_functions = test_*
-
-# Directories to search for tests
-testpaths = tests
-
-# Output options
 addopts =
     -v
     --strict-markers
     --tb=short
-    --color=yes
-    --maxfail=5
-
-# Markers for categorizing tests
 markers =
-    unit: Unit tests for individual components
-    integration: Integration tests for service interactions
-    slow: Tests that take longer to run
-    requires_models: Tests that require PaddleOCR models
-
-# Coverage options (optional)
-# addopts = --cov=app --cov-report=html --cov-report=term
-
-# Logging
-log_cli = false
-log_cli_level = INFO
+    unit: Unit tests
+    integration: Integration tests
+    slow: Slow running tests