Keep logs for a set number of days

Logs grew forever. A daily prune-logs cron now deletes entries older
than the app setting logs_keep_days (Settings > General, super admin;
default AppData.LogsKeepDays, 90), with an index on logs.created_at.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/dict/log-categories.ts

@@ -23,4 +23,10 @@ export const LogCategories = [
         title: "Error",
         value: "error",
     },
-] as const;
+] as const;
+
+/**
+ * The app setting (Settings > General) for how many days logs are kept,
+ * else `AppData.LogsKeepDays`.
+ */
+export const LogsKeepDaysSettingKey = "logs_keep_days";