Beta: clean up servers that opted out while the bot was offline

The bot remembers where it registered beta commands (beta_registered) and
removes them from servers that are no longer in the beta at the next start.
Failed cleanups are retried; a server the bot has left is forgotten.

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

internal/db/repos/settingsrepo/repo.go

@@ -441,3 +441,37 @@ func (r *Repo) ListBetaGuilds(ctx context.Context) ([]string, error) {
 	}
 	return out, rows.Err()
 }
+
+// ListBetaRegistered returns the servers where the bot registered beta
+// commands, so it can clean up after itself even if a server opted out while
+// it was offline.
+func (r *Repo) ListBetaRegistered(ctx context.Context) ([]string, error) {
+	rows, err := r.db.QueryContext(ctx, `SELECT guild_id FROM beta_registered`)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var out []string
+	for rows.Next() {
+		var id int64
+		if err := rows.Scan(&id); err != nil {
+			return nil, err
+		}
+		out = append(out, strconv.FormatInt(id, 10))
+	}
+	return out, rows.Err()
+}
+
+// SetBetaRegistered records (or forgets) that beta commands exist in a server.
+func (r *Repo) SetBetaRegistered(ctx context.Context, guildID string, registered bool) error {
+	id, err := strconv.ParseInt(guildID, 10, 64)
+	if err != nil {
+		return err
+	}
+	if registered {
+		_, err = r.db.ExecContext(ctx, `INSERT INTO beta_registered (guild_id) VALUES ($1) ON CONFLICT DO NOTHING`, id)
+	} else {
+		_, err = r.db.ExecContext(ctx, `DELETE FROM beta_registered WHERE guild_id = $1`, id)
+	}
+	return err
+}