전체 UI 색상 통일 - 제각각이던 빨강/주황/파랑 계열을 의미별 토큰 4종으로 정리

danger/warning/success/approved(+각 Bg 버전)를 AppPalette에 추가하고,
화면마다 다르게 쓰이던 Colors.red[400/600/700]/redAccent, orange/amber
계열, blue 계열 리터럴을 전부 해당 토큰으로 교체. NFC 체크인 화면의
홀로 튀던 Colors.blueAccent도 함께 정리.

lib/ui/teacher_attendance_page.dart

@@ -360,8 +360,10 @@ class _TeacherAttendancePageState extends State<TeacherAttendancePage> {
     final bool isPending = student['attendanceStatus'] == 'PENDING';
     final bool isComplete = student['attendanceStatus'] == 'COMPLETE';
     final Color statusColor = hasViolation
-        ? Colors.red
-        : (isPending ? Colors.orange : (isComplete ? Colors.blue : Colors.red));
+        ? AppPalette.danger
+        : (isPending
+              ? AppPalette.warning
+              : (isComplete ? AppPalette.approved : AppPalette.danger));
     final String statusLine = hasViolation
         ? '무단반출 (${student['violationTime']})'
         : (isPending
@@ -373,10 +375,10 @@ class _TeacherAttendancePageState extends State<TeacherAttendancePage> {
     return Container(
       padding: const EdgeInsets.all(14),
       decoration: BoxDecoration(
-        color: hasViolation ? Colors.red[50] : AppPalette.paper,
+        color: hasViolation ? AppPalette.dangerBg : AppPalette.paper,
         borderRadius: BorderRadius.circular(20),
         border: Border.all(
-          color: hasViolation ? Colors.red[300]! : AppPalette.sage,
+          color: hasViolation ? AppPalette.danger : AppPalette.sage,
           width: hasViolation ? 1.5 : 1,
         ),
         boxShadow: [
@@ -451,10 +453,10 @@ class _TeacherAttendancePageState extends State<TeacherAttendancePage> {
             overflow: TextOverflow.ellipsis,
             style: TextStyle(
               color: hasViolation
-                  ? Colors.red[700]
+                  ? AppPalette.danger
                   : (isPending
-                        ? Colors.orange[800]
-                        : (isComplete ? Colors.grey[600] : Colors.red[400])),
+                        ? AppPalette.warning
+                        : (isComplete ? Colors.grey[600] : AppPalette.danger)),
               fontSize: 11.5,
               fontWeight: hasViolation ? FontWeight.bold : FontWeight.normal,
             ),
@@ -470,7 +472,7 @@ class _TeacherAttendancePageState extends State<TeacherAttendancePage> {
                   student['studentName'],
                 ),
                 style: ElevatedButton.styleFrom(
-                  backgroundColor: Colors.red[600],
+                  backgroundColor: AppPalette.danger,
                   foregroundColor: Colors.white,
                   padding: EdgeInsets.zero,
                 ),
@@ -781,18 +783,18 @@ class _TeacherAttendancePageState extends State<TeacherAttendancePage> {
     final bool isPending = student['attendanceStatus'] == 'PENDING';
     final bool isComplete = student['attendanceStatus'] == 'COMPLETE';
     final Color background = hasViolation
-        ? Colors.red[50]!
+        ? AppPalette.dangerBg
         : isComplete
-        ? Colors.blue[50]!
+        ? AppPalette.approvedBg
         : isPending
-        ? Colors.orange[50]!
+        ? AppPalette.warningBg
         : AppPalette.paper;
     final Color border = hasViolation
-        ? Colors.red[300]!
+        ? AppPalette.danger
         : isComplete
-        ? Colors.blue[200]!
+        ? AppPalette.approved
         : isPending
-        ? Colors.orange[200]!
+        ? AppPalette.warning
         : AppPalette.sage;
 
     return InkWell(
@@ -828,7 +830,7 @@ class _TeacherAttendancePageState extends State<TeacherAttendancePage> {
                 '무단반출',
                 style: TextStyle(
                   fontSize: 7.5,
-                  color: Colors.red[700],
+                  color: AppPalette.danger,
                   fontWeight: FontWeight.bold,
                 ),
               ),
@@ -849,19 +851,19 @@ class _TeacherAttendancePageState extends State<TeacherAttendancePage> {
       margin: const EdgeInsets.fromLTRB(16, 8, 16, 0),
       padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 10),
       decoration: BoxDecoration(
-        color: Colors.amber[100],
+        color: AppPalette.warningBg,
         borderRadius: BorderRadius.circular(12),
-        border: Border.all(color: Colors.amber[400]!),
+        border: Border.all(color: AppPalette.warning),
       ),
       child: Row(
         children: [
-          Icon(Icons.lock_open_rounded, color: Colors.amber[800], size: 20),
+          Icon(Icons.lock_open_rounded, color: AppPalette.warning, size: 20),
           const SizedBox(width: 8),
           Expanded(
             child: Text(
               '지금 전체 반출 허용 중입니다 ($until 까지) — 이 시간 동안은 무단반출 경고가 뜨지 않아요.',
               style: TextStyle(
-                color: Colors.amber[900],
+                color: AppPalette.warning,
                 fontWeight: FontWeight.bold,
                 fontSize: 12.5,
               ),