Beta servers: testers can use beta features in servers whose owner opted in

- beta.Configure takes the opted-in servers; testers are looked up in the beta server
- beta commands registered per opted-in server and removed when it opts out
- beta.ServerEnabled for behaviour that no person triggers
- docs updated

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

internal/db/repos/settingsrepo/repo.go

@@ -422,3 +422,22 @@ func (r *Repo) GetBetaSettings(ctx context.Context) (guildID, roleID string, err
 	}
 	return guildID, roleID, nil
 }
+
+// ListBetaGuilds returns the servers whose owner opted in to beta features
+// (set on the dashboard), as ID strings.
+func (r *Repo) ListBetaGuilds(ctx context.Context) ([]string, error) {
+	rows, err := r.db.QueryContext(ctx, `SELECT guild_id FROM beta_guilds ORDER BY enabled_at`)
+	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()
+}