Disable legacy HTTP image hooks by default

hook/hook.php

@@ -2,6 +2,15 @@
 
 namespace sammo\img_service;
 
+header('Content-Type: application/json');
+if (!file_exists(__DIR__.'/legacy-enabled')) {
+    http_response_code(410);
+    die(json_encode([
+        'result'=>false,
+        'reason'=>'legacy hook disabled',
+    ]));
+}
+
 include(__DIR__.'/gogs_key.php');