fix: use HTTP for remote signaling server (no TLS configured)

The remote server at synced-relay.duckdns.org:9876 serves plain HTTP.
The previous https:// URL caused "failed to fetch" on room creation.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: notd5a

frontend/src/config.ts

@@ -14,7 +14,7 @@ const MODE_KEY = "synced_server_mode";
 const URL_KEY = "synced_signaling_url";
 
 /** Default remote signaling server — always used for remote mode. */
-export const DEFAULT_REMOTE_URL = "https://synced-relay.duckdns.org:9876";
+export const DEFAULT_REMOTE_URL = "http://synced-relay.duckdns.org:9876";
 
 export function getServerMode(): ServerMode {
   const stored = localStorage.getItem(MODE_KEY);