feat: implement task management module

Backend (FastAPI):
- Database migration for spaces, projects, task_statuses, tasks tables
- SQLAlchemy models with relationships
- Pydantic schemas for CRUD operations
- Spaces API: CRUD with soft delete
- Projects API: CRUD with auto-created default statuses
- Tasks API: CRUD, status change, assign, subtask support
- Permission middleware with Security Level filtering
- Subtask depth limit (max 2 levels)

Frontend (React + Vite):
- Layout component with navigation
- Spaces list page
- Projects list page
- Tasks list page with status management

Fixes:
- auth_client.py: use 'username' field for external API
- config.py: extend JWT expiry to 7 days
- auth/router.py: sync Redis session with JWT expiry

Tests: 36 passed (unit + integration)
E2E: All APIs verified with real authentication

OpenSpec: add-task-management archived

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

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

backend/app/main.py

@@ -4,6 +4,9 @@ from fastapi.middleware.cors import CORSMiddleware
 from app.api.auth import router as auth_router
 from app.api.users import router as users_router
 from app.api.departments import router as departments_router
+from app.api.spaces import router as spaces_router
+from app.api.projects import router as projects_router
+from app.api.tasks import router as tasks_router
 from app.core.config import settings
 
 app = FastAPI(
@@ -25,6 +28,9 @@ app.add_middleware(
 app.include_router(auth_router.router, prefix="/api/auth", tags=["Authentication"])
 app.include_router(users_router.router, prefix="/api/users", tags=["Users"])
 app.include_router(departments_router.router, prefix="/api/departments", tags=["Departments"])
+app.include_router(spaces_router)
+app.include_router(projects_router)
+app.include_router(tasks_router)
 
 
 @app.get("/health")