[AC-AISVC-65~AC-AISVC-70] Intent recognition with keyword and regex matching
- Add IntentRule SQLModel entity with tenant isolation
- Implement IntentRuleService for CRUD operations with hit statistics
- Implement IntentRouter matching engine (priority DESC, keyword then regex)
- Add rule caching by tenant_id with TTL=60s and CRUD invalidation
- Add intent rules management API (POST/GET/PUT/DELETE /admin/intent-rules)
- Support four response types: fixed/rag/flow/transfer
T12.6 (Orchestrator integration) and T12.7 (unit tests) pending for integration phase
MerCry