feat: complete issue fixes and implement remaining features

## Critical Issues (CRIT-001~003) - All Fixed
- JWT secret key validation with pydantic field_validator
- Login audit logging for success/failure attempts
- Frontend API path prefix removal

## High Priority Issues (HIGH-001~008) - All Fixed
- Project soft delete using is_active flag
- Redis session token bytes handling
- Rate limiting with slowapi (5 req/min for login)
- Attachment API permission checks
- Kanban view with drag-and-drop
- Workload heatmap UI (WorkloadPage, WorkloadHeatmap)
- TaskDetailModal integrating Comments/Attachments
- UserSelect component for task assignment

## Medium Priority Issues (MED-001~012) - All Fixed
- MED-001~005: DB commits, N+1 queries, datetime, error format, blocker flag
- MED-006: Project health dashboard (HealthService, ProjectHealthPage)
- MED-007: Capacity update API (PUT /api/users/{id}/capacity)
- MED-008: Schedule triggers (cron parsing, deadline reminders)
- MED-009: Watermark feature (image/PDF watermarking)
- MED-010~012: useEffect deps, DOM operations, PDF export

## New Files
- backend/app/api/health/ - Project health API
- backend/app/services/health_service.py
- backend/app/services/trigger_scheduler.py
- backend/app/services/watermark_service.py
- backend/app/core/rate_limiter.py
- frontend/src/pages/ProjectHealthPage.tsx
- frontend/src/components/ProjectHealthCard.tsx
- frontend/src/components/KanbanBoard.tsx
- frontend/src/components/WorkloadHeatmap.tsx

## Tests
- 113 new tests passing (health: 32, users: 14, triggers: 35, watermark: 32)

## OpenSpec Archives
- add-project-health-dashboard
- add-capacity-update-api
- add-schedule-triggers
- add-watermark-feature
- add-rate-limiting
- enhance-frontend-ux
- add-resource-management-ui

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/tests/test_rate_limit.py

@@ -0,0 +1,124 @@
+"""
+Test suite for rate limiting functionality.
+
+Tests the rate limiting feature on the login endpoint to ensure
+protection against brute force attacks.
+"""
+
+import pytest
+from unittest.mock import patch, MagicMock, AsyncMock
+
+from app.services.auth_client import AuthAPIError
+
+
+class TestRateLimiting:
+    """Test rate limiting on the login endpoint."""
+
+    def test_login_rate_limit_exceeded(self, client):
+        """
+        Test that the login endpoint returns 429 after exceeding rate limit.
+
+        GIVEN a client IP has made 5 login attempts within 1 minute
+        WHEN the client attempts another login
+        THEN the system returns HTTP 429 Too Many Requests
+        AND the response includes a Retry-After header
+        """
+        # Mock the external auth service to return auth error
+        with patch("app.api.auth.router.verify_credentials", new_callable=AsyncMock) as mock_verify:
+            mock_verify.side_effect = AuthAPIError("Invalid credentials")
+
+            login_data = {"email": "test@example.com", "password": "wrongpassword"}
+
+            # Make 5 requests (the limit)
+            for i in range(5):
+                response = client.post("/api/auth/login", json=login_data)
+                # These should fail due to invalid credentials (401), but not rate limit
+                assert response.status_code == 401, f"Request {i+1} expected 401, got {response.status_code}"
+
+            # The 6th request should be rate limited
+            response = client.post("/api/auth/login", json=login_data)
+            assert response.status_code == 429, f"Expected 429 Too Many Requests, got {response.status_code}"
+
+            # Response should contain error details
+            data = response.json()
+            assert "error" in data or "detail" in data, "Response should contain error details"
+
+    def test_login_within_rate_limit(self, client):
+        """
+        Test that requests within the rate limit are allowed.
+
+        GIVEN a client IP has not exceeded the rate limit
+        WHEN the client makes login requests
+        THEN the requests are processed normally (not rate limited)
+        """
+        with patch("app.api.auth.router.verify_credentials", new_callable=AsyncMock) as mock_verify:
+            mock_verify.side_effect = AuthAPIError("Invalid credentials")
+
+            login_data = {"email": "test@example.com", "password": "wrongpassword"}
+
+            # Make requests within the limit
+            for i in range(3):
+                response = client.post("/api/auth/login", json=login_data)
+                # These should fail due to invalid credentials (401), but not be rate limited
+                assert response.status_code == 401, f"Request {i+1} expected 401, got {response.status_code}"
+
+    def test_rate_limit_response_format(self, client):
+        """
+        Test that the 429 response format matches API standards.
+
+        GIVEN the rate limit has been exceeded
+        WHEN the client receives a 429 response
+        THEN the response body contains appropriate error information
+        """
+        with patch("app.api.auth.router.verify_credentials", new_callable=AsyncMock) as mock_verify:
+            mock_verify.side_effect = AuthAPIError("Invalid credentials")
+
+            login_data = {"email": "test@example.com", "password": "wrongpassword"}
+
+            # Exhaust the rate limit
+            for _ in range(5):
+                client.post("/api/auth/login", json=login_data)
+
+            # The next request should be rate limited
+            response = client.post("/api/auth/login", json=login_data)
+
+            assert response.status_code == 429
+
+            # Check response body contains error information
+            data = response.json()
+            assert "error" in data or "detail" in data, "Response should contain error details"
+
+
+class TestRateLimiterConfiguration:
+    """Test rate limiter configuration."""
+
+    def test_limiter_uses_redis_storage(self):
+        """
+        Test that the limiter is configured with Redis storage.
+
+        GIVEN the rate limiter configuration
+        WHEN we inspect the storage URI
+        THEN it should be configured to use Redis
+        """
+        from app.core.rate_limiter import limiter
+        from app.core.config import settings
+
+        # The limiter should be configured
+        assert limiter is not None
+
+        # Verify Redis URL is properly configured
+        assert settings.REDIS_URL.startswith("redis://")
+
+    def test_limiter_uses_remote_address_key(self):
+        """
+        Test that the limiter uses client IP as the key.
+
+        GIVEN the rate limiter configuration
+        WHEN we check the key function
+        THEN it should use get_remote_address
+        """
+        from app.core.rate_limiter import limiter
+        from slowapi.util import get_remote_address
+
+        # The key function should be get_remote_address
+        assert limiter._key_func == get_remote_address