Add FastAPI hello-world structure with Docker and DB health check

- app/main.py: root endpoint + /health that reports DB connectivity
- app/db.py: pymysql connection check from MYSQL_* env vars, logged at startup
- Dockerfile: python:3.12-slim, port 8720
- docker-compose.yml: mysql:8.2 with healthcheck, app waits for DB ready
- requirements.txt: fastapi, uvicorn, pymysql

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/main.py

@@ -0,0 +1,34 @@
+import logging
+from contextlib import asynccontextmanager
+
+from fastapi import FastAPI
+
+from app.db import check_db
+
+logger = logging.getLogger("pops")
+
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    if check_db():
+        logger.info("Database connection OK")
+    else:
+        logger.warning("Database unreachable — check MYSQL_* environment variables")
+    yield
+
+
+app = FastAPI(title="POPS", lifespan=lifespan)
+
+
+@app.get("/")
+def root():
+    return {"message": "Hello from POPS"}
+
+
+@app.get("/health")
+def health():
+    db_ok = check_db()
+    return {
+        "status": "ok" if db_ok else "degraded",
+        "db": "connected" if db_ok else "unreachable",
+    }