학생 계정 개별 추가: 기본 비밀번호 1234로 고정

엑셀 일괄 등록과 동일하게 초기 비밀번호를 항상 1234로 고정하고
입력칸을 없앰. 대신 폼에 "초기 비밀번호: 1234 (고정)" 안내 표시.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

lib/ui/teacher_student_management_page.dart

@@ -27,7 +27,6 @@ class _TeacherStudentManagementPageState
       TeacherStudentManagementController();
   final TextEditingController _addIdController = TextEditingController();
   final TextEditingController _addNameController = TextEditingController();
-  final TextEditingController _addPwController = TextEditingController();
   int? _selectedGrade;
   bool _isDragging = false;
 
@@ -42,17 +41,15 @@ class _TeacherStudentManagementPageState
     _controller.dispose();
     _addIdController.dispose();
     _addNameController.dispose();
-    _addPwController.dispose();
     super.dispose();
   }
 
-  // ➕ [학생 추가 버튼 동작]
+  // ➕ [학생 추가 버튼 동작] 기본 비밀번호는 항상 1234로 고정.
   Future<void> _addStudentAccount() async {
     final sId = _addIdController.text.trim();
     final sName = _addNameController.text.trim();
-    final sPw = _addPwController.text.trim();
 
-    if (sId.isEmpty || sName.isEmpty || sPw.isEmpty) {
+    if (sId.isEmpty || sName.isEmpty) {
       ScaffoldMessenger.of(
         context,
       ).showSnackBar(const SnackBar(content: Text('⚠️ 모든 입력란을 채워주세요.')));
@@ -62,14 +59,13 @@ class _TeacherStudentManagementPageState
     final (success, message) = await _controller.addStudentAccount(
       studentId: sId,
       name: sName,
-      password: sPw,
+      password: '1234',
       grade: _selectedGrade,
     );
     if (!mounted) return;
     if (success) {
       _addIdController.clear();
       _addNameController.clear();
-      _addPwController.clear();
       setState(() => _selectedGrade = null);
     }
     ScaffoldMessenger.of(
@@ -430,11 +426,18 @@ class _TeacherStudentManagementPageState
               decoration: fieldDecoration('이름', Icons.person),
             ),
             const SizedBox(height: 4),
-            TextField(
-              controller: _addPwController,
-              obscureText: true,
-              style: const TextStyle(fontSize: 12),
-              decoration: fieldDecoration('초기 비밀번호', Icons.lock),
+            const Padding(
+              padding: EdgeInsets.symmetric(horizontal: 4),
+              child: Row(
+                children: [
+                  Icon(Icons.lock, size: 14, color: Colors.grey),
+                  SizedBox(width: 6),
+                  Text(
+                    '초기 비밀번호: 1234 (고정)',
+                    style: TextStyle(fontSize: 11, color: Colors.grey),
+                  ),
+                ],
+              ),
             ),
             const SizedBox(height: 4),
             DropdownButtonFormField<int>(