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.

src/screens/profile/AccountDeletionScreen.tsx

@@ -1,3 +1,4 @@
+import { StatusBar } from 'expo-status-bar';
 import React, { useCallback, useEffect, useMemo, useState } from 'react';
 import {
   ActivityIndicator,
@@ -13,7 +14,7 @@ import { MaterialCommunityIcons } from '@expo/vector-icons';
 import { useRouter } from 'expo-router';
 import { authService } from '../../services';
 import { spacing, borderRadius, fontSizes, useAppColors, type AppColors } from '../../theme';
-import { Text } from '../../components/common';
+import { Text, SimpleHeader } from '../../components/common';
 import { useResponsive, useResponsiveSpacing } from '../../hooks';
 import { useAuthStore } from '../../stores';
 import type { DeletionStatusDTO } from '../../types/dto';
@@ -275,7 +276,7 @@ export const AccountDeletionScreen: React.FC = () => {
 
   if (loading) {
     return (
-      <SafeAreaView style={styles.container} edges={['bottom']}>
+      <SafeAreaView style={styles.container} edges={['top', 'bottom']}>
         <View style={styles.loadingWrap}>
           <ActivityIndicator size="large" color={colors.primary.main} />
         </View>
@@ -284,7 +285,9 @@ export const AccountDeletionScreen: React.FC = () => {
   }
 
   return (
-    <SafeAreaView style={styles.container} edges={['bottom']}>
+    <SafeAreaView style={styles.container} edges={['top', 'bottom']}>
+      <StatusBar style="auto" />
+      <SimpleHeader title="注销账号" onBack={() => router.back()} />
       <ScrollView contentContainerStyle={[styles.scrollContent, { paddingBottom: scrollBottomInset, paddingHorizontal: responsivePadding }]}>
         <View style={styles.content}>
           {status?.is_pending_deletion ? (