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/conftest.py

@@ -1,3 +1,8 @@
+import os
+
+# Set testing environment before importing app modules
+os.environ["TESTING"] = "true"
+
 import pytest
 from fastapi.testclient import TestClient
 from sqlalchemy import create_engine
@@ -103,6 +108,18 @@ def mock_redis():
 @pytest.fixture(scope="function")
 def client(db, mock_redis):
     """Create test client with overridden dependencies."""
+    # Reset rate limiter storage before each test
+    from app.core.rate_limiter import limiter
+    if hasattr(limiter, '_storage') and limiter._storage:
+        try:
+            limiter._storage.reset()
+        except Exception:
+            pass  # Memory storage might not have reset method
+    # For memory storage, clear internal state
+    if hasattr(limiter, '_limiter') and hasattr(limiter._limiter, '_storage'):
+        storage = limiter._limiter._storage
+        if hasattr(storage, 'storage'):
+            storage.storage.clear()
 
     def override_get_db():
         try: