refactor(layout): 统一 z-index 配置

- layoutConfig.js: 添加 Z_INDEX.FOOTER (1000，与 NAVBAR 同级)
- HomeNavbar.js: zIndex 从硬编码 1000 改为 Z_INDEX.NAVBAR
- AppFooter.js: 添加 zIndex={Z_INDEX.FOOTER}

导航栏和页脚的 z-index 现在统一在 layoutConfig.js 中配置。

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/components/Navbars/HomeNavbar.js

@@ -55,7 +55,7 @@ import { useProfileCompleteness } from '../../hooks/useProfileCompleteness';
 import NavbarActions from './components/NavbarActions';
 
 // 布局配置
-import { LAYOUT_PADDING } from '../../layouts/config/layoutConfig';
+import { LAYOUT_PADDING, Z_INDEX } from '../../layouts/config/layoutConfig';
 
 // Phase 4: MoreNavMenu 和 NavItems 组件已提取到 Navigation 目录
 
@@ -146,7 +146,7 @@ export default function HomeNavbar() {
                 top={showCompletenessAlert ? "60px" : 0}
                 left={0}
                 right={0}
-                zIndex={1000}
+                zIndex={Z_INDEX.NAVBAR}
                 bg={navbarBg}
                 backdropFilter="blur(10px)"
                 borderBottom="1px"

src/layouts/AppFooter.js

@@ -1,7 +1,7 @@
 import React from 'react';
 import { Box, VStack, HStack, Text, Link, useColorModeValue } from '@chakra-ui/react';
 import RiskDisclaimer from '../components/RiskDisclaimer';
-import { LAYOUT_PADDING } from './config/layoutConfig';
+import { LAYOUT_PADDING, Z_INDEX } from './config/layoutConfig';
 
 /**
  * 应用通用页脚组件
@@ -9,7 +9,7 @@ import { LAYOUT_PADDING } from './config/layoutConfig';
  */
 const AppFooter = () => {
   return (
-    <Box bg={useColorModeValue('gray.100', 'gray.800')} py={2} px={LAYOUT_PADDING.x}>
+    <Box bg={useColorModeValue('gray.100', 'gray.800')} py={2} px={LAYOUT_PADDING.x} zIndex={Z_INDEX.FOOTER} position="relative">
         <VStack spacing={1}>
           <RiskDisclaimer />
           <Text color="gray.500" fontSize="sm">

src/layouts/config/layoutConfig.js

@@ -40,6 +40,7 @@ export const Z_INDEX = {
 
     // === 导航相关 (1000-1499) ===
     NAVBAR: 1000,           // 顶部导航栏
+    FOOTER: 1000,           // 页脚（与导航栏同级）
     CONNECTION_STATUS: 1050, // 连接状态栏
     PROFILE_ALERT: 1100,    // 个人资料提示