refactor(ui): implement custom header system and unify screen layouts

Refactor the navigation and header strategy by replacing native stack headers with a custom `SimpleHeader` component across most profile and detail screens. This provides a more consistent UI/UX and better control over layout behavior.

- Implement `SimpleHeader` component in `src/components/common`.
- Disable native header rendering in `app/(app)/(tabs)/profile/_layout.tsx` and `app/_layout.tsx`.
- Update profile sub-screens to use `SimpleHeader` and `StatusBar` from `expo-status-bar`.
- Refactor `PostDetailScreen` to use a custom header implementation for better integration with the post author information.
- Update `UserScreen` to wrap content in `SafeAreaView` with the new header.
- Adjust `AppBackButton` to support transparent backgrounds.

app/(app)/(tabs)/profile/_layout.tsx

@@ -1,49 +1,28 @@
-import { useMemo } from 'react';
 import { Stack } from 'expo-router';
-import { useRouter } from 'expo-router';
-
-import { AppBackButton } from '../../../../src/components/common';
-import { useAppColors } from '../../../../src/theme';
 
 export default function ProfileStackLayout() {
-  const router = useRouter();
-  const colors = useAppColors();
-
-  const headerOptions = useMemo(
-    () => ({
-      headerStyle: { backgroundColor: colors.background.paper },
-      headerTintColor: colors.text.primary,
-      headerTitleStyle: { fontWeight: '600' as const },
-      headerShadowVisible: false,
-      headerBackTitle: '',
-    }),
-    [colors]
-  );
-
   return (
     <Stack
       screenOptions={{
-        ...headerOptions,
-        headerBackVisible: false,
-        headerLeft: () => <AppBackButton onPress={() => router.back()} />,
+        headerShown: false,
       }}
     >
-      <Stack.Screen name="index" options={{ headerShown: false }} />
-      <Stack.Screen name="settings" options={{ headerShown: true, title: '设置' }} />
-      <Stack.Screen name="edit-profile" options={{ title: '编辑资料' }} />
-      <Stack.Screen name="account-security" options={{ title: '账号安全' }} />
-      <Stack.Screen name="my-posts" options={{ title: '我的帖子' }} />
-      <Stack.Screen name="bookmarks" options={{ title: '收藏' }} />
-      <Stack.Screen name="notification-settings" options={{ title: '通知设置' }} />
-      <Stack.Screen name="blocked-users" options={{ title: '黑名单' }} />
-      <Stack.Screen name="chat-settings" options={{ title: '聊天设置' }} />
-      <Stack.Screen name="about" options={{ title: '关于我们' }} />
-      <Stack.Screen name="terms" options={{ title: '用户协议' }} />
-      <Stack.Screen name="privacy" options={{ title: '隐私政策' }} />
-      <Stack.Screen name="verification" options={{ title: '身份认证' }} />
-      <Stack.Screen name="data-storage" options={{ title: '数据与存储' }} />
-      <Stack.Screen name="privacy-settings" options={{ title: '隐私设置' }} />
-      <Stack.Screen name="account-deletion" options={{ title: '注销账号' }} />
+      <Stack.Screen name="index" />
+      <Stack.Screen name="settings" />
+      <Stack.Screen name="edit-profile" />
+      <Stack.Screen name="account-security" />
+      <Stack.Screen name="my-posts" />
+      <Stack.Screen name="bookmarks" />
+      <Stack.Screen name="notification-settings" />
+      <Stack.Screen name="blocked-users" />
+      <Stack.Screen name="chat-settings" />
+      <Stack.Screen name="about" />
+      <Stack.Screen name="terms" />
+      <Stack.Screen name="privacy" />
+      <Stack.Screen name="verification" />
+      <Stack.Screen name="data-storage" />
+      <Stack.Screen name="privacy-settings" />
+      <Stack.Screen name="account-deletion" />
     </Stack>
   );
 }