fix: Strip markdown fences from Gemini JSON response to fix PDF curriculum extraction

backend/scripts/curriculum_worker.php

@@ -209,9 +209,17 @@ if ($code !== 200 || empty($res)) {
 
 $jsonResponse = json_decode($res, true);
 $text = $jsonResponse['candidates'][0]['content']['parts'][0]['text'] ?? '';
+
+// Clean up markdown fences if Gemini returned them
+$text = preg_replace('/^```json\s*/i', '', $text);
+$text = preg_replace('/```\s*$/i', '', $text);
+$text = trim($text);
+
 $parsedStructure = json_decode($text, true);
 
 if (empty($parsedStructure) || empty($parsedStructure['units'])) {
+    // Log the actual text for debugging
+    file_put_contents($stateFile . '.debug.txt', $text);
     updateState($stateFile, 'error', 0, 'فشل الذكاء الاصطناعي في إرجاع بنية JSON صالحة.');
     return;
 }