feat: 迁移珊瑚橙主题体系并新增认证基础组件（ADR-005）

- app_theme.dart 重写为语义 token（AppColors/AppRadius），落地 primaryStrong/error 等 AA 对比度色
- 五个页面与公共组件的旧靛蓝硬编码色值全部替换为 token，仅换色不动布局
- 新增 BrandMark/AppTextField/PrimaryButton/InlineErrorBanner/AuthScaffold 及 6 个 widget 测试
- 门禁：dart format（0 changed）/ flutter analyze（0 issues）/ flutter test（7 passed）

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

lib/features/profile/profile_page.dart

@@ -82,10 +82,10 @@ class ProfilePage extends StatelessWidget {
               const SizedBox(height: 5),
               const Text(
                 'Patbond 社区创作达人',
-                style: TextStyle(color: Color(0xFFA5B4FC), fontSize: 12),
+                style: TextStyle(color: AppColors.accent, fontSize: 12),
               ),
               const SizedBox(height: 20),
-              const Divider(color: Color(0xFF334155)),
+              const Divider(color: Colors.white24),
               const SizedBox(height: 10),
               Row(
                 mainAxisAlignment: MainAxisAlignment.spaceAround,
@@ -108,7 +108,7 @@ class ProfilePage extends StatelessWidget {
             children: menuItems.map((item) {
               return ListTile(
                 leading: CircleAvatar(
-                  backgroundColor: const Color(0xFFEEF2FF),
+                  backgroundColor: AppColors.surfaceTint,
                   child: Icon(item.$1, color: AppColors.primary),
                 ),
                 title: Text(
@@ -162,7 +162,7 @@ class _ProfileStat extends StatelessWidget {
         const SizedBox(height: 3),
         Text(
           label,
-          style: const TextStyle(color: Color(0xFF94A3B8), fontSize: 11),
+          style: const TextStyle(color: Colors.white70, fontSize: 11),
         ),
       ],
     );