feat: adopt material 3 theme and billing adjustments

lib/widgets/common/form_fields/date_picker_field.dart

@@ -1,6 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:intl/intl.dart';
-import '../../../theme/app_colors.dart';
+// import '../../../theme/app_colors.dart';
 import '../../../l10n/app_localizations.dart';
 
 /// 날짜 선택 필드 위젯
@@ -48,10 +48,10 @@ class DatePickerField extends StatelessWidget {
       children: [
         Text(
           label,
-          style: const TextStyle(
+          style: TextStyle(
             fontSize: 16,
             fontWeight: FontWeight.w600,
-            color: AppColors.darkNavy,
+            color: Theme.of(context).colorScheme.onSurface,
           ),
         ),
         const SizedBox(height: 8),
@@ -67,13 +67,14 @@ class DatePickerField extends StatelessWidget {
                     lastDate: lastDate ??
                         DateTime.now().add(const Duration(days: 365 * 10)),
                     builder: (BuildContext context, Widget? child) {
+                      final cs = Theme.of(context).colorScheme;
                       return Theme(
-                        data: ThemeData.light().copyWith(
-                          colorScheme: ColorScheme.light(
+                        data: Theme.of(context).copyWith(
+                          colorScheme: cs.copyWith(
                             primary: effectivePrimaryColor,
-                            onPrimary: Colors.white,
-                            surface: Colors.white,
-                            onSurface: Colors.black,
+                            onPrimary: cs.onPrimary,
+                            surface: cs.surface,
+                            onSurface: cs.onSurface,
                           ),
                         ),
                         child: child!,
@@ -90,10 +91,13 @@ class DatePickerField extends StatelessWidget {
           child: Container(
             padding: contentPadding ?? const EdgeInsets.all(16),
             decoration: BoxDecoration(
-              color: backgroundColor ?? AppColors.surfaceColorAlt,
+              color: backgroundColor ?? Theme.of(context).colorScheme.surface,
               borderRadius: BorderRadius.circular(16),
               border: Border.all(
-                color: AppColors.borderColor.withValues(alpha: 0.7),
+                color: Theme.of(context)
+                    .colorScheme
+                    .outline
+                    .withValues(alpha: 0.6),
                 width: 1.5,
               ),
             ),
@@ -105,15 +109,18 @@ class DatePickerField extends StatelessWidget {
                         .format(selectedDate),
                     style: TextStyle(
                       fontSize: 16,
-                      color:
-                          enabled ? AppColors.textPrimary : AppColors.textMuted,
+                      color: enabled
+                          ? Theme.of(context).colorScheme.onSurface
+                          : Theme.of(context).colorScheme.onSurfaceVariant,
                     ),
                   ),
                 ),
                 Icon(
                   Icons.calendar_today,
                   size: 20,
-                  color: enabled ? AppColors.navyGray : AppColors.textMuted,
+                  color: enabled
+                      ? Theme.of(context).colorScheme.onSurfaceVariant
+                      : Theme.of(context).colorScheme.onSurfaceVariant,
                 ),
               ],
             ),
@@ -214,13 +221,14 @@ class _DateRangeItem extends StatelessWidget {
                 firstDate: firstDate,
                 lastDate: lastDate,
                 builder: (BuildContext context, Widget? child) {
+                  final cs = Theme.of(context).colorScheme;
                   return Theme(
-                    data: ThemeData.light().copyWith(
-                      colorScheme: ColorScheme.light(
+                    data: Theme.of(context).copyWith(
+                      colorScheme: cs.copyWith(
                         primary: effectivePrimaryColor,
-                        onPrimary: Colors.white,
-                        surface: Colors.white,
-                        onSurface: Colors.black,
+                        onPrimary: cs.onPrimary,
+                        surface: cs.surface,
+                        onSurface: cs.onSurface,
                       ),
                     ),
                     child: child!,
@@ -237,10 +245,10 @@ class _DateRangeItem extends StatelessWidget {
       child: Container(
         padding: const EdgeInsets.all(16),
         decoration: BoxDecoration(
-          color: AppColors.surfaceColorAlt,
+          color: Theme.of(context).colorScheme.surface,
           borderRadius: BorderRadius.circular(16),
           border: Border.all(
-            color: AppColors.borderColor.withValues(alpha: 0.7),
+            color: Theme.of(context).colorScheme.outline.withValues(alpha: 0.6),
             width: 1.5,
           ),
         ),
@@ -249,9 +257,9 @@ class _DateRangeItem extends StatelessWidget {
           children: [
             Text(
               label,
-              style: const TextStyle(
+              style: TextStyle(
                 fontSize: 12,
-                color: AppColors.textSecondary,
+                color: Theme.of(context).colorScheme.onSurfaceVariant,
               ),
             ),
             const SizedBox(height: 4),
@@ -263,8 +271,9 @@ class _DateRangeItem extends StatelessWidget {
               style: TextStyle(
                 fontSize: 16,
                 fontWeight: FontWeight.w500,
-                color:
-                    date != null ? AppColors.textPrimary : AppColors.textMuted,
+                color: date != null
+                    ? Theme.of(context).colorScheme.onSurface
+                    : Theme.of(context).colorScheme.onSurfaceVariant,
               ),
             ),
           ],