feat(ai-services): add Python FastAPI AI/ML services container

Create libs/ai-services/ with FastAPI app providing:
- POST /avm/predict — XGBoost-backed property price prediction (heuristic fallback)
- POST /avm/extract-features — Vietnamese NLP feature extraction from listing text
- POST /moderation/check — content moderation with rule-based flagging
- GET /health — health check endpoint

Includes Dockerfile (Python 3.12), docker-compose integration, Pydantic models,
and 9 passing tests covering all endpoints.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

libs/ai-services/app/routers/moderation.py

@@ -0,0 +1,12 @@
+from fastapi import APIRouter
+
+from app.models.moderation import ModerationRequest, ModerationResponse
+from app.services.moderation_service import moderation_service
+
+router = APIRouter(prefix="/moderation", tags=["Moderation"])
+
+
+@router.post("/check", response_model=ModerationResponse)
+def check(req: ModerationRequest) -> ModerationResponse:
+    """Check text content for policy violations."""
+    return moderation_service.check(req)