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>
   );
 }

app/_layout.tsx

@@ -19,7 +19,7 @@ import {
   usePaperThemeFromStore,
   useResolvedColorScheme,
 } from '../src/theme';
-import { AppBackButton } from '../src/components/common';
+
 import AppPromptBar from '../src/components/common/AppPromptBar';
 import AppDialogHost from '../src/components/common/AppDialogHost';
 import { installAlertOverride } from '@/services/ui';
@@ -232,7 +232,6 @@ function APKUpdateBootstrap() {
 
 function ThemedStack() {
   const router = useRouter();
-  const colors = useAppColors();
   const resolved = useResolvedColorScheme();
 
   return (
@@ -250,49 +249,25 @@ function ThemedStack() {
           <Stack.Screen
             name="terms"
             options={{
-              headerShown: true,
-              title: '用户协议',
-              headerStyle: { backgroundColor: colors.background.paper },
-              headerTintColor: colors.text.primary,
-              headerShadowVisible: false,
-              headerBackVisible: false,
-              headerLeft: () => <AppBackButton onPress={() => router.back()} />,
+              headerShown: false,
             }}
           />
           <Stack.Screen
             name="privacy"
             options={{
-              headerShown: true,
-              title: '隐私政策',
-              headerStyle: { backgroundColor: colors.background.paper },
-              headerTintColor: colors.text.primary,
-              headerShadowVisible: false,
-              headerBackVisible: false,
-              headerLeft: () => <AppBackButton onPress={() => router.back()} />,
+              headerShown: false,
             }}
           />
           <Stack.Screen
             name="post/[postId]"
             options={{
-              headerShown: true,
-              title: '',
-              // 与 PostDetailScreen 的 SafeAreaView（background.default）同色，避免出现 header/内容之间的色差线
-              headerStyle: { backgroundColor: colors.background.default },
-              headerTintColor: colors.text.primary,
-              headerShadowVisible: false,
-              headerBackVisible: false,
-              headerLeft: () => <AppBackButton onPress={() => router.back()} />,
+              headerShown: false,
             }}
           />
           <Stack.Screen
             name="user/[userId]"
             options={{
-              headerShown: true,
-              title: '用户主页',
-              headerStyle: { backgroundColor: colors.background.paper },
-              headerTintColor: colors.text.primary,
-              headerBackVisible: false,
-              headerLeft: () => <AppBackButton onPress={() => router.back()} />,
+              headerShown: false,
             }}
           />
         </Stack>