feat: adopt material 3 theme and billing adjustments

lib/screens/app_lock_screen.dart

@@ -1,7 +1,7 @@
 import 'package:flutter/material.dart';
 import 'package:provider/provider.dart';
 import '../providers/app_lock_provider.dart';
-import '../theme/app_colors.dart';
+// import '../theme/app_colors.dart';
 
 class AppLockScreen extends StatelessWidget {
   const AppLockScreen({super.key});
@@ -13,26 +13,26 @@ class AppLockScreen extends StatelessWidget {
         child: Column(
           mainAxisAlignment: MainAxisAlignment.center,
           children: [
-            const Icon(
+            Icon(
               Icons.lock_outline,
               size: 80,
-              color: AppColors.navyGray,
+              color: Theme.of(context).colorScheme.onSurfaceVariant,
             ),
             const SizedBox(height: 24),
-            const Text(
+            Text(
               '앱이 잠겨 있습니다',
               style: TextStyle(
                 fontSize: 24,
                 fontWeight: FontWeight.bold,
-                color: AppColors.darkNavy,
+                color: Theme.of(context).colorScheme.onSurface,
               ),
             ),
             const SizedBox(height: 16),
-            const Text(
+            Text(
               '생체 인증으로 잠금을 해제하세요',
               style: TextStyle(
                 fontSize: 16,
-                color: AppColors.navyGray,
+                color: Theme.of(context).colorScheme.onSurfaceVariant,
               ),
             ),
             const SizedBox(height: 32),
@@ -41,15 +41,16 @@ class AppLockScreen extends StatelessWidget {
                 final appLock = context.read<AppLockProvider>();
                 final success = await appLock.authenticate();
                 if (!success && context.mounted) {
+                  final cs = Theme.of(context).colorScheme;
                   ScaffoldMessenger.of(context).showSnackBar(
-                    const SnackBar(
+                    SnackBar(
                       content: Text(
                         '인증에 실패했습니다. 다시 시도해주세요.',
                         style: TextStyle(
-                          color: AppColors.pureWhite,
+                          color: cs.onPrimary,
                         ),
                       ),
-                      backgroundColor: AppColors.dangerColor,
+                      backgroundColor: cs.error,
                     ),
                   );
                 }