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>

README.md

@@ -69,6 +69,10 @@ Once running, access the web UI at [http://localhost:8000](http://localhost:8000
 | `PIRATS_LOG_FILE` | _(unset)_ | If set, also write logs to this file (rotating, 10 MB × 5 backups). Logs always go to stderr regardless. |
 | `PIRATS_LOG_LEVEL` | `INFO` | Minimum log severity (`DEBUG`/`INFO`/`WARNING`/`ERROR`/`CRITICAL`). |
 | `PIRATS_DEV_MODE` | _(unset = on)_ | Default Dev Mode for new games. Unset is treated as a local checkout (on); set to `0`/`false` to disable. |
+| `PIRATS_PURGE_ENABLED` | `true` | Periodically purge old finished/inactive games. |
+| `PIRATS_PURGE_INTERVAL_HOURS` | `24` | How often the purge task runs. |
+| `PIRATS_PURGE_FINISHED_DAYS` | `14` | Purge games that finished more than this many days ago. |
+| `PIRATS_PURGE_INACTIVE_DAYS` | `30` | Purge games with no activity for this many days. |
 
 ---
 
@@ -111,6 +115,12 @@ services.pirats = {
   logFile = "/var/log/pirats/pirats.log"; # rotating; stderr also goes to the journal
   logLevel = "info";
   openFirewall = false; # Set to true to open ports in the firewall
+  purge = {
+    enable = true;       # periodically remove old finished/inactive games
+    intervalHours = 24;
+    finishedDays = 14;   # purge games finished more than 14 days ago
+    inactiveDays = 30;   # ...or with no activity for 30 days
+  };
 };
 ```