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/config.py

@@ -0,0 +1,13 @@
+from pydantic_settings import BaseSettings
+
+
+class Settings(BaseSettings):
+    app_name: str = "Goodgo AI Services"
+    debug: bool = False
+    model_path: str = "/app/models"
+    log_level: str = "info"
+
+    model_config = {"env_prefix": "AI_"}
+
+
+settings = Settings()