fix: Auto-seed official subjects table to satisfy foreign key constraints on courses creation

backend/app/Services/CurriculumService.php

@@ -17,7 +17,23 @@ class CurriculumService
         if (self::$schemaChecked) return;
 
         try {
-            // Check if lessons table has timeline_chapters_json column
+            // 1. Check if subjects table has data, seed if empty
+            $subjectsCount = (int)(Database::selectOne("SELECT COUNT(*) as total FROM subjects")['total'] ?? 0);
+            if ($subjectsCount === 0) {
+                Database::query(
+                    "INSERT INTO subjects (id, name, code, stream, is_active) VALUES
+                     (1, 'الرياضيات العلمي', 'math_scientific', 'scientific', 1),
+                     (2, 'الثقافة العسكرية والتربية الوطنية', 'military_culture', 'common', 1),
+                     (3, 'الفيزياء', 'physics_scientific', 'scientific', 1),
+                     (4, 'الكيمياء', 'chemistry_scientific', 'scientific', 1),
+                     (5, 'العلوم الحياتية (الأحياء)', 'biology_scientific', 'scientific', 1),
+                     (6, 'اللغة الإنجليزية', 'english_common', 'common', 1),
+                     (7, 'اللغة العربية المشتركة', 'arabic_common', 'common', 1)
+                     ON DUPLICATE KEY UPDATE name = VALUES(name)"
+                );
+            }
+
+            // 2. Check if lessons table has timeline_chapters_json column
             $cols = Database::select("SHOW COLUMNS FROM lessons LIKE 'timeline_chapters_json'");
             if (empty($cols)) {
                 Database::query("ALTER TABLE lessons ADD COLUMN timeline_chapters_json JSON NULL AFTER hls_url");