feat: implement audit trail module

- Backend (FastAPI):
  - AuditLog and AuditAlert models with Alembic migration
  - AuditService with SHA-256 checksum for log integrity
  - AuditMiddleware for request metadata extraction (IP, user_agent)
  - Integrated audit logging into Task, Project, Blocker APIs
  - Query API with filtering, pagination, CSV export
  - Integrity verification endpoint
  - Sensitive operation alerts with acknowledgement

- Frontend (React + Vite):
  - Admin AuditPage with filters and export
  - ResourceHistory component for change tracking
  - Audit service for API calls

- Testing:
  - 15 tests covering service and API endpoints

- OpenSpec:
  - add-audit-trail change archived

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

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

backend/app/main.py

@@ -1,6 +1,7 @@
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 
+from app.middleware.audit import AuditMiddleware
 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
@@ -12,6 +13,7 @@ from app.api.comments import router as comments_router
 from app.api.notifications import router as notifications_router
 from app.api.blockers import router as blockers_router
 from app.api.websocket import router as websocket_router
+from app.api.audit import router as audit_router
 from app.core.config import settings
 
 app = FastAPI(
@@ -29,6 +31,9 @@ app.add_middleware(
     allow_headers=["*"],
 )
 
+# Audit middleware - extracts request metadata for audit logging
+app.add_middleware(AuditMiddleware)
+
 # Include routers
 app.include_router(auth_router.router, prefix="/api/auth", tags=["Authentication"])
 app.include_router(users_router.router, prefix="/api/users", tags=["Users"])
@@ -41,6 +46,7 @@ app.include_router(comments_router)
 app.include_router(notifications_router)
 app.include_router(blockers_router)
 app.include_router(websocket_router)
+app.include_router(audit_router)
 
 
 @app.get("/health")