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/nfc_poccket_checkin_screen.dart

@@ -50,9 +50,9 @@ class _NfcPocketCheckInScreenState extends State<NfcPocketCheckInScreen> {
   void _handleMessage(String text, WatchMessageLevel level) {
     final Color color = switch (level) {
       WatchMessageLevel.info => Colors.blueGrey,
-      WatchMessageLevel.success => Colors.green,
-      WatchMessageLevel.warning => Colors.orange,
-      WatchMessageLevel.error => Colors.red,
+      WatchMessageLevel.success => AppPalette.success,
+      WatchMessageLevel.warning => AppPalette.warning,
+      WatchMessageLevel.error => AppPalette.danger,
     };
     _showSnackBar(text, color);
   }
@@ -73,10 +73,13 @@ class _NfcPocketCheckInScreenState extends State<NfcPocketCheckInScreen> {
     showDialog(
       context: context,
       builder: (context) => AlertDialog(
-        backgroundColor: Colors.red[50],
+        backgroundColor: AppPalette.dangerBg,
         title: const Text(
           "무단 반출 감지",
-          style: TextStyle(color: Colors.red, fontWeight: FontWeight.bold),
+          style: TextStyle(
+            color: AppPalette.danger,
+            fontWeight: FontWeight.bold,
+          ),
         ),
         content: Text(
           "[${pocketNumber ?? _controller.activePocketNumber}] 주머니에서 휴대폰이 꺼내진 것으로 감지되었습니다.\n담당 선생님께 알림이 전송되었습니다.",
@@ -177,8 +180,8 @@ class _NfcPocketCheckInScreenState extends State<NfcPocketCheckInScreen> {
                     _controller.isProcessing ? Icons.sync : Icons.nfc,
                     size: 100,
                     color: _controller.isProcessing
-                        ? Colors.orange
-                        : Colors.blueAccent,
+                        ? AppPalette.warning
+                        : AppPalette.ink,
                   ),
                   const SizedBox(height: 30),
 
@@ -190,7 +193,7 @@ class _NfcPocketCheckInScreenState extends State<NfcPocketCheckInScreen> {
                       fontSize: 18,
                       fontWeight: FontWeight.bold,
                       color: _controller.isProcessing
-                          ? Colors.orange
+                          ? AppPalette.warning
                           : Colors.black87,
                     ),
                   ),
@@ -227,13 +230,13 @@ class _NfcPocketCheckInScreenState extends State<NfcPocketCheckInScreen> {
                 height: 160,
                 decoration: BoxDecoration(
                   shape: BoxShape.circle,
-                  color: Colors.greenAccent.withValues(alpha: 0.15),
-                  border: Border.all(color: Colors.greenAccent, width: 3),
+                  color: AppPalette.success.withValues(alpha: 0.15),
+                  border: Border.all(color: AppPalette.success, width: 3),
                 ),
                 child: const Icon(
                   Icons.shield_rounded,
                   size: 72,
-                  color: Colors.greenAccent,
+                  color: AppPalette.success,
                 ),
               ),
               const SizedBox(height: 40),