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/main.py

@@ -0,0 +1,28 @@
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+
+from app.config import settings
+from app.routers import avm, moderation
+
+app = FastAPI(
+    title=settings.app_name,
+    version="0.1.0",
+    docs_url="/docs",
+    redoc_url="/redoc",
+)
+
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=["*"],
+    allow_credentials=True,
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+app.include_router(avm.router)
+app.include_router(moderation.router)
+
+
+@app.get("/health")
+def health() -> dict:
+    return {"status": "ok", "service": settings.app_name}