선생님 대시보드에 학년 필터 칩 추가

출석자/미출석자 필터처럼 학년 전체/1학년/2학년/3학년 칩을 추가해서
선택한 학년만 볼 수 있게 함. 상태 필터와 조합해서 같이 적용됨.

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

lib/ui/teacher_attendance_page.dart

@@ -706,24 +706,56 @@ class _TeacherAttendancePageState extends State<TeacherAttendancePage> {
   Widget _buildFilterChips() {
     return Padding(
       padding: const EdgeInsets.symmetric(vertical: 8, horizontal: 16),
-      child: Row(
+      child: Column(
+        crossAxisAlignment: CrossAxisAlignment.start,
         children: [
-          FilterChip(
-            label: const Text("전체"),
-            selected: _controller.filterType == "ALL",
-            onSelected: (_) => _controller.setFilter("ALL"),
+          Wrap(
+            spacing: 8,
+            runSpacing: 8,
+            children: [
+              FilterChip(
+                label: const Text("전체"),
+                selected: _controller.filterType == "ALL",
+                onSelected: (_) => _controller.setFilter("ALL"),
+              ),
+              FilterChip(
+                label: const Text("🟢 출석자"),
+                selected: _controller.filterType == "CHECKED_IN",
+                onSelected: (_) => _controller.setFilter("CHECKED_IN"),
+              ),
+              FilterChip(
+                label: const Text("🔴 미출석자"),
+                selected: _controller.filterType == "ABSENT",
+                onSelected: (_) => _controller.setFilter("ABSENT"),
+              ),
+            ],
           ),
-          const SizedBox(width: 8),
-          FilterChip(
-            label: const Text("🟢 출석자"),
-            selected: _controller.filterType == "CHECKED_IN",
-            onSelected: (_) => _controller.setFilter("CHECKED_IN"),
-          ),
-          const SizedBox(width: 8),
-          FilterChip(
-            label: const Text("🔴 미출석자"),
-            selected: _controller.filterType == "ABSENT",
-            onSelected: (_) => _controller.setFilter("ABSENT"),
+          const SizedBox(height: 8),
+          Wrap(
+            spacing: 8,
+            runSpacing: 8,
+            children: [
+              ChoiceChip(
+                label: const Text("학년 전체"),
+                selected: _controller.gradeFilter == "ALL",
+                onSelected: (_) => _controller.setGradeFilter("ALL"),
+              ),
+              ChoiceChip(
+                label: const Text("1학년"),
+                selected: _controller.gradeFilter == "1",
+                onSelected: (_) => _controller.setGradeFilter("1"),
+              ),
+              ChoiceChip(
+                label: const Text("2학년"),
+                selected: _controller.gradeFilter == "2",
+                onSelected: (_) => _controller.setGradeFilter("2"),
+              ),
+              ChoiceChip(
+                label: const Text("3학년"),
+                selected: _controller.gradeFilter == "3",
+                onSelected: (_) => _controller.setGradeFilter("3"),
+              ),
+            ],
           ),
         ],
       ),