feat(Theme): enhance theming and UI consistency across components

- Updated app.json to set userInterfaceStyle to automatic for improved theme adaptability.
- Refactored layout components to utilize useAppColors for dynamic theming, ensuring consistent color usage.
- Introduced SystemChrome component to manage system UI background color based on theme.
- Enhanced TabsLayout, ProfileStackLayout, and other components to leverage new theming structure.
- Improved QRCodeScanner, SearchBar, and CommentItem styles to align with the updated theme system.
- Consolidated styles in SystemMessageItem and TabBar for better maintainability and visual coherence.

src/theme/tokens.ts

@@ -0,0 +1,60 @@
+/**
+ * 与明暗无关的设计 token
+ */
+
+export const fontSizes = {
+  xs: 10,
+  sm: 12,
+  md: 14,
+  lg: 16,
+  xl: 18,
+  '2xl': 20,
+  '3xl': 24,
+  '4xl': 30,
+};
+
+export const spacing = {
+  xs: 4,
+  sm: 8,
+  md: 12,
+  lg: 16,
+  xl: 20,
+  '2xl': 24,
+  '3xl': 32,
+  '4xl': 40,
+  '5xl': 48,
+  '6xl': 56,
+};
+
+export const borderRadius = {
+  sm: 4,
+  md: 8,
+  lg: 12,
+  xl: 16,
+  '2xl': 24,
+  full: 9999,
+};
+
+export const shadows = {
+  sm: {
+    shadowColor: '#000',
+    shadowOffset: { width: 0, height: 1 },
+    shadowOpacity: 0.18,
+    shadowRadius: 1.0,
+    elevation: 1,
+  },
+  md: {
+    shadowColor: '#000',
+    shadowOffset: { width: 0, height: 2 },
+    shadowOpacity: 0.22,
+    shadowRadius: 2.22,
+    elevation: 3,
+  },
+  lg: {
+    shadowColor: '#000',
+    shadowOffset: { width: 0, height: 4 },
+    shadowOpacity: 0.3,
+    shadowRadius: 4.65,
+    elevation: 6,
+  },
+};