Periodic purge of old finished/inactive games

New maintenance.py runs a background asyncio loop (started from the app
lifespan) that purges games which either finished more than PIRATS_PURGE_
FINISHED_DAYS (default 14) ago or have had no activity for PIRATS_PURGE_
INACTIVE_DAYS (default 30). "Activity" is a game's most-recent GameEvent
timestamp; games with no events are undatable and left alone.

Each purge is logged with the crew name, uuid, reason, idle days and an
estimated byte footprint; every run that removes anything VACUUMs the SQLite
file and logs the disk space actually reclaimed. Child rows go via the ORM
cascade already declared on Game's relationships.

Configurable via PIRATS_PURGE_ENABLED / _INTERVAL_HOURS / _FINISHED_DAYS /
_INACTIVE_DAYS, exposed as services.pirats.purge.* in the NixOS module and
documented in the README. Unit test covers the selection logic and cascade;
smoke-tested the VACUUM/reclaim path against a file DB.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/pirats/main.py

@@ -1,3 +1,5 @@
+import asyncio
+import contextlib
 from contextlib import asynccontextmanager
 from typing import Optional
 from fastapi import FastAPI, Form, Depends, HTTPException, APIRouter, WebSocket, WebSocketDisconnect
@@ -14,6 +16,7 @@ import os
 from pathlib import Path
 
 from . import crud
+from . import maintenance
 from .database import run_migrations, get_session, engine
 from .ws import manager
 
@@ -73,7 +76,20 @@ async def lifespan(app: FastAPI):
     )
     run_migrations()
     logger.info("Database migrations applied")
+
+    purge_cfg = maintenance.purge_config()
+    purge_task = None
+    if purge_cfg.enabled:
+        purge_task = asyncio.create_task(maintenance.purge_loop(purge_cfg))
+    else:
+        logger.info("Game purge task disabled (PIRATS_PURGE_ENABLED)")
+
     yield
+
+    if purge_task is not None:
+        purge_task.cancel()
+        with contextlib.suppress(asyncio.CancelledError):
+            await purge_task
     logger.info("Shutting down")
 
 app = FastAPI(title="Rats with Gats Remote Play API", lifespan=lifespan)