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/data/app-data.ts

@@ -278,6 +278,13 @@ export const AppData = {
     BotHookMaxEventsPerRun: 20,
     BotHookEventsKeepDays: 30,
     BotHookEventsKeepDaysMax: 3650,
+    /**
+     * Logs (Activity) are deleted after this many days by the daily
+     * `prune-logs` cron: the default, with the most an install may set
+     * (`logs_keep_days`, Settings > General).
+     */
+    LogsKeepDays: 90,
+    LogsKeepDaysMax: 3650,
     /**
      * How many hook calls a list loads at once, and how much of each call's
      * payload and response a list shows (the whole of both opens on one).