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/home/home_page.dart

@@ -132,7 +132,7 @@ class _HomePageState extends State<HomePage>
                       Text(
                         '充值',
                         style: GoogleFonts.spaceGrotesk(
-                          fontSize: 24,
+                          fontSize: 16,
                           fontWeight: FontWeight.bold,
                           color: colorScheme.onSurface,
                         ),
@@ -251,7 +251,7 @@ class _HomePageState extends State<HomePage>
                   Text(
                     '充值申请成功',
                     style: GoogleFonts.spaceGrotesk(
-                      fontSize: 20,
+                      fontSize: 16,
                       fontWeight: FontWeight.bold,
                       color: colorScheme.onSurface,
                     ),
@@ -350,7 +350,7 @@ class _HomePageState extends State<HomePage>
             children: [
               Text(title,
                   style: GoogleFonts.spaceGrotesk(
-                    fontSize: 20,
+                    fontSize: 16,
                     fontWeight: FontWeight.bold,
                     color: colorScheme.onSurface,
                   )),
@@ -469,7 +469,7 @@ class _GreetingSection extends StatelessWidget {
               style: TextStyle(
                 color: colorScheme.onSurface,
                 fontWeight: FontWeight.bold,
-                fontSize: 24,
+                fontSize: 18,
               ),
             ),
           ],
@@ -644,7 +644,7 @@ class _AssetCardState extends State<_AssetCard> {
           Text(
             displayAsset,
             style: GoogleFonts.spaceGrotesk(
-              fontSize: 32,
+              fontSize: 22,
               fontWeight: FontWeight.bold,
               color: colorScheme.onSurface,
             ),
@@ -1103,7 +1103,7 @@ class _HoldingsSection extends StatelessWidget {
               style: TextStyle(
                 color: colorScheme.onSurface,
                 fontWeight: FontWeight.bold,
-                fontSize: 18,
+                fontSize: 16,
               ),
             ),
             TextButton(
@@ -1116,7 +1116,7 @@ class _HoldingsSection extends StatelessWidget {
                 children: [
                   Text('资产详情',
                       style: TextStyle(
-                          fontWeight: FontWeight.bold, fontSize: 14)),
+                          fontWeight: FontWeight.bold, fontSize: 13)),
                   const SizedBox(width: 4),
                   Icon(LucideIcons.chevronRight,
                       size: 16, color: colorScheme.primary),
@@ -1157,7 +1157,7 @@ class _EmptyHoldings extends StatelessWidget {
             style: TextStyle(
               color: colorScheme.onSurface,
               fontWeight: FontWeight.w600,
-              fontSize: 16,
+              fontSize: 14,
             ),
           ),
           SizedBox(height: AppSpacing.sm),
@@ -1165,7 +1165,7 @@ class _EmptyHoldings extends StatelessWidget {
             '快去交易吧~',
             style: TextStyle(
               color: colorScheme.onSurfaceVariant,
-              fontSize: 14,
+              fontSize: 13,
             ),
           ),
         ],
@@ -1245,7 +1245,7 @@ class _HoldingItem extends StatelessWidget {
                       style: TextStyle(
                         color: colorScheme.onSurface,
                         fontWeight: FontWeight.bold,
-                        fontSize: 16,
+                        fontSize: 14,
                       )),
                   Text(holding.quantity,
                       style: TextStyle(
@@ -1263,7 +1263,7 @@ class _HoldingItem extends StatelessWidget {
                   style: TextStyle(
                     color: colorScheme.onSurface,
                     fontWeight: FontWeight.w500,
-                    fontSize: 14,
+                    fontSize: 13,
                   )),
               Text(holding.formattedProfitRate,
                   style: TextStyle(
@@ -1439,7 +1439,7 @@ class _ProfitStatCard extends StatelessWidget {
                 ? '${isProfit ? '+' : ''}${value!.toStringAsFixed(2)}'
                 : '--',
             style: GoogleFonts.spaceGrotesk(
-              fontSize: 15,
+              fontSize: 14,
               fontWeight: FontWeight.bold,
               color: color,
             ),