Fix double URL-encoding of Matrix user ID in SynapseHelper

rawurlencode($username) was called on line 38 (encoding the username),
then rawurlencode($matrixId) was called on line 39 encoding the already-
encoded string — causing %20 to become %2520 for usernames with special
characters. Fixed by building $matrixId with the plain username and only
encoding the full Matrix ID once in the URL path.

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

helpers/SynapseHelper.php

@@ -35,7 +35,10 @@ class SynapseHelper {
             return null;
         }
 
-        $matrixId = '@' . rawurlencode($username) . ':' . $domain;
+        // Build the Matrix user ID and percent-encode it once for the URL path.
+        // rawurlencode($username) here would double-encode any special chars when
+        // the full $matrixId string is encoded again below.
+        $matrixId = '@' . $username . ':' . $domain;
         $url      = rtrim($baseUrl, '/') . '/_synapse/admin/v2/users/' . rawurlencode($matrixId);
 
         $ch = curl_init($url);