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>

public/index.php

@@ -910,8 +910,12 @@ if (str_starts_with($route, '/api/')) {
                     ],
                     CURLOPT_TIMEOUT => 5,
                 ]);
-                curl_exec($bch);
+                $bRes = curl_exec($bch);
+                $bStat = curl_getinfo($bch, CURLINFO_HTTP_CODE);
                 curl_close($bch);
+                @error_log('[hyprcrd] sync-event POST → ' . $senderName
+                    . ' status=' . $bStat
+                    . ' body=' . substr((string)$bRes, 0, 120));
             }
 
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