앱 전체 배경/카드 색상을 coolors 팔레트로 통일

coolors.co 무채색 팔레트(1c1c1c-daddd8-ecebe4-eef0f2-fafaff)를
lib/theme/app_palette.dart에 정의하고, 로그인/대시보드/출석 확인/
학생 계정 관리/스마트기기 반출(신청·대장)/관리자 화면 전반의
배너·배경·카드·기본 버튼 색을 이 팔레트로 교체.

기능적으로 의미 있는 색(위반/미출석/삭제/거절 등 경고성 빨간색,
승인 대기 등 상태 표시)은 그대로 유지 — 구조적/장식적 색상만
무채색으로 통일해 위험한 동작이 시각적으로 더 도드라지게 함.

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

lib/ui/teacher_attendance_page.dart

@@ -2,6 +2,7 @@
 // 서버 통신·상태·파생 로직은 lib/function/teacher_attendance_controller.dart가 담당한다.
 import 'package:flutter/material.dart';
 import '../function/teacher_attendance_controller.dart';
+import '../theme/app_palette.dart';
 
 // -----------------------------------------------------------------------------
 // 📅 [서브 화면 1] 실시간 출석 확인 란 (StudentDashboard 카드 스타일 리스트화)
@@ -202,13 +203,13 @@ class _TeacherAttendancePageState extends State<TeacherAttendancePage> {
         final int absentCount = totalCount - checkedInCount;
 
         return Scaffold(
-          backgroundColor: Colors.grey[100],
+          backgroundColor: AppPalette.mist,
           appBar: AppBar(
             title: const Text(
               '📋 실시간 출석 현황',
               style: TextStyle(fontWeight: FontWeight.bold),
             ),
-            backgroundColor: Colors.blue,
+            backgroundColor: AppPalette.ink,
             foregroundColor: Colors.white,
             elevation: 0,
             actions: [
@@ -336,7 +337,7 @@ class _TeacherAttendancePageState extends State<TeacherAttendancePage> {
                     width: 4,
                     height: 16,
                     decoration: BoxDecoration(
-                      color: Colors.blue,
+                      color: AppPalette.ink,
                       borderRadius: BorderRadius.circular(2),
                     ),
                   ),
@@ -346,7 +347,7 @@ class _TeacherAttendancePageState extends State<TeacherAttendancePage> {
                     style: const TextStyle(
                       fontSize: 16,
                       fontWeight: FontWeight.bold,
-                      color: Colors.black87,
+                      color: AppPalette.ink,
                     ),
                   ),
                   const SizedBox(width: 6),
@@ -396,11 +397,12 @@ class _TeacherAttendancePageState extends State<TeacherAttendancePage> {
     return Container(
       padding: const EdgeInsets.all(14),
       decoration: BoxDecoration(
-        color: hasViolation ? Colors.red[50] : Colors.white,
+        color: hasViolation ? Colors.red[50] : AppPalette.paper,
         borderRadius: BorderRadius.circular(20),
-        border: hasViolation
-            ? Border.all(color: Colors.red[300]!, width: 1.5)
-            : null,
+        border: Border.all(
+          color: hasViolation ? Colors.red[300]! : AppPalette.sage,
+          width: hasViolation ? 1.5 : 1,
+        ),
         boxShadow: [
           BoxShadow(
             color: Colors.black.withValues(alpha: 0.03),
@@ -590,7 +592,7 @@ class _TeacherAttendancePageState extends State<TeacherAttendancePage> {
     return Container(
       padding: const EdgeInsets.all(20),
       decoration: BoxDecoration(
-        color: Colors.white,
+        color: AppPalette.paper,
         borderRadius: BorderRadius.circular(16),
         boxShadow: [
           BoxShadow(
@@ -639,7 +641,7 @@ class _TeacherAttendancePageState extends State<TeacherAttendancePage> {
     return Container(
       width: double.infinity,
       padding: const EdgeInsets.all(16),
-      color: const Color(0xFF1E293B),
+      color: AppPalette.ink,
       child: Row(
         mainAxisAlignment: MainAxisAlignment.spaceAround,
         children: [