diag: error_log sync-event POSTs to trace missing toasts

Temporary diagnostic scaffolding — B-side logs every POST to the relay
(status + body snippet), A-side already console.debugs the GET result
via sync_debug. Lets us narrow down where the sender-side toast gets
lost.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

config.php

@@ -1,7 +1,7 @@
 <?php
 
 define('APP_NAME', 'hyprcrd');
-define('APP_VERSION', '1.8.1');
+define('APP_VERSION', '1.8.2');
 
 // Database path — writable directory, outside webroot
 // DB_PATH / UPLOAD_DIR can be pre-defined by the Electron router for app isolation