refactor: 优化字号主题体系，参考成熟交易平台标准

- 重构主题字号体系 (h1-h4, body, amount等)
- 修复16个页面文件中的硬编码字号
- 新字号层级参考币安/OKX标准
- Display: 22/20/18px (总资产、价格)
- Headline: 15/14/13px (标题、副标题)
- Body: 13/12/11px (正文、辅助文字)
- Label: 11/10/9px (标签)
- Number: 22/16/13px (数字)

flutter_monisuo/lib/ui/pages/mine/kyc_page.dart

@@ -112,7 +112,7 @@ class _KycPageState extends State<KycPage> {
                           Text(
                             '身份验证',
                             style: GoogleFonts.spaceGrotesk(
-                              fontSize: 20,
+                              fontSize: 16,
                               fontWeight: FontWeight.bold,
                               color: colorScheme.onSurface,
                             ),

flutter_monisuo/lib/ui/pages/mine/mine_page.dart

@@ -109,7 +109,7 @@ class _MinePageState extends State<MinePage> with AutomaticKeepAliveClientMixin
       builder: (context) => ShadDialog(
         title: Row(
           children: [
-            _AppLogo(radius: 20, fontSize: 20),
+            _AppLogo(radius: 20, fontSize: 16),
             SizedBox(width: AppSpacing.sm + AppSpacing.xs),
             const Text('模拟所'),
           ],
@@ -196,7 +196,7 @@ class _UserCard extends StatelessWidget {
                     ),
                   ],
                 ),
-                child: _AppLogo(radius: 36, fontSize: 28, text: user?.avatarText),
+                child: _AppLogo(radius: 36, fontSize: 20, text: user?.avatarText),
               ),
               // 验证徽章
               Positioned(
@@ -229,7 +229,7 @@ class _UserCard extends StatelessWidget {
                 Text(
                   user?.username ?? '未登录',
                   style: GoogleFonts.spaceGrotesk(
-                    fontSize: 24,
+                    fontSize: 16,
                     fontWeight: FontWeight.bold,
                     color: colorScheme.onSurface,
                   ),