feat(TextComponent): enhance text styling with dynamic font weights and improved layout

- Updated Text component to support dynamic font weights, allowing for more flexible text styling.
- Refactored variant styles to utilize new font weight constants for better consistency across text variants.
- Introduced letter spacing adjustments for improved readability and visual appeal.
- Added font family configuration for iOS and Android to optimize typography across platforms.

src/theme/tokens.ts

@@ -2,6 +2,39 @@
  * 与明暗无关的设计 token
  */
 
+// 字体配置 - 使用系统字体栈，优化字重
+export const fontFamily = {
+  // iOS 系统字体
+  ios: {
+    regular: 'System',
+    medium: 'System',
+    semibold: 'System',
+    bold: 'System',
+  },
+  // Android 系统字体
+  android: {
+    regular: 'Roboto',
+    medium: 'Roboto',
+    semibold: 'Roboto',
+    bold: 'Roboto',
+  },
+  // 通用字体栈
+  system: {
+    regular: 'System',
+    medium: 'System',
+    semibold: 'System',
+    bold: 'System',
+  },
+};
+
+// 字体字重 - 使用数值更精确控制
+export const fontWeights = {
+  regular: '400' as const,
+  medium: '500' as const,
+  semibold: '600' as const,
+  bold: '700' as const,
+};
+
 export const fontSizes = {
   xs: 10,
   sm: 12,