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/tests/test_health.py

@@ -0,0 +1,12 @@
+from fastapi.testclient import TestClient
+
+from app.main import app
+
+client = TestClient(app)
+
+
+def test_health():
+    resp = client.get("/health")
+    assert resp.status_code == 200
+    data = resp.json()
+    assert data["status"] == "ok"