feat: Phase 3 - AES encryption, SQL audit engine, audit logs (85 tests)

Phase 3.1: Instance password AES-256-GCM encryption
Phase 3.2: SQL audit rule engine (10 rules)
Phase 3.3: Auto-audit on ticket creation
Phase 3.4: Operation audit logs + GET /audit/logs
Tests: 44 -> 85 (41 new), Frontend: AuditLogsPage

backend/app/api/v1/router.py

@@ -1,6 +1,6 @@
 from fastapi import APIRouter
 
-from app.api.v1.endpoints import auth, user, instance, ticket, query, dashboard
+from app.api.v1.endpoints import auth, user, instance, ticket, query, dashboard, audit
 
 api_router = APIRouter(prefix="/api/v1")
 
@@ -10,3 +10,4 @@ api_router.include_router(instance.router)
 api_router.include_router(ticket.router)
 api_router.include_router(query.router)
 api_router.include_router(dashboard.router)
+api_router.include_router(audit.router)