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>

docker-compose.yml

@@ -0,0 +1,29 @@
+services:
+  db:
+    image: mysql:8.2
+    restart: unless-stopped
+    env_file: .env
+    volumes:
+      - mysql_data:/var/lib/mysql
+      - ./db.sql:/docker-entrypoint-initdb.d/01_schema.sql
+    healthcheck:
+      test: ["CMD", "mysqladmin", "ping", "-h", "127.0.0.1", "--silent"]
+      interval: 10s
+      timeout: 5s
+      retries: 10
+      start_period: 30s
+
+  app:
+    build: .
+    ports:
+      - "8720:8720"
+    env_file: .env
+    environment:
+      MYSQL_HOST: db      # override localhost → compose service name
+    depends_on:
+      db:
+        condition: service_healthy
+    restart: unless-stopped
+
+volumes:
+  mysql_data: