chore(prod): startup migrations, readiness checks and backend healthcheck

- add backend entrypoint that can run alembic upgrade head on startup
- add RUN_MIGRATIONS_ON_STARTUP setting and compose wiring
- add /health/live and /health/ready endpoints with db+redis checks
- add backend container healthcheck against readiness endpoint
- document readiness and startup migration behavior

app/config/settings.py

@@ -8,6 +8,7 @@ class Settings(BaseSettings):
     debug: bool = True
     api_v1_prefix: str = "/api/v1"
     auto_create_tables: bool = True
+    run_migrations_on_startup: bool = False
 
     secret_key: str = Field(default="change-me-please-12345", min_length=16)
     access_token_expire_minutes: int = 30