fix: 资产卡片金额自适应缩放，防止换行

flutter_monisuo/lib/ui/pages/asset/components/balance_card.dart

@@ -35,16 +35,24 @@ class BalanceCard extends StatelessWidget {
               ),
             ),
             const SizedBox(height: 12),
-            Text(
-              _formatBalance(displayBalance),
-              style: AppTextStyles.numberLarge(context),
+            FittedBox(
+              fit: BoxFit.scaleDown,
+              alignment: Alignment.centerLeft,
+              child: Text(
+                _formatBalance(displayBalance),
+                style: AppTextStyles.numberLarge(context),
+              ),
             ),
-            const SizedBox(height: 12),
-            Text(
-              '\u2248 \$${_formatBalance(displayBalance)} USD',
-              style: AppTextStyles.bodyMedium(context).copyWith(
-                color: context.appColors.onSurfaceMuted,
-                fontWeight: FontWeight.w400,
+            const SizedBox(height: 8),
+            FittedBox(
+              fit: BoxFit.scaleDown,
+              alignment: Alignment.centerLeft,
+              child: Text(
+                '\u2248 \$${_formatBalance(displayBalance)} USD',
+                style: AppTextStyles.bodyMedium(context).copyWith(
+                  color: context.appColors.onSurfaceMuted,
+                  fontWeight: FontWeight.w400,
+                ),
               ),
             ),
           ],