refactor(layout): 统一布局边距配置，改用百分比

- layoutConfig.js: LAYOUT_PADDING.x 改为 { base: 4, md: 6, lg: '12%' }
- HomeNavbar.js: 导入 LAYOUT_PADDING，替换硬编码边距
- AppFooter.js: 导入 LAYOUT_PADDING，替换硬编码边距

现在导航栏、内容区、页脚统一使用 LAYOUT_PADDING.x 配置，
修改边距只需调整 layoutConfig.js 一处即可全局生效。

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

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

src/components/Navbars/HomeNavbar.js

@@ -54,6 +54,9 @@ import ProfileCompletenessAlert from './components/ProfileCompletenessAlert';
 import { useProfileCompleteness } from '../../hooks/useProfileCompleteness';
 import NavbarActions from './components/NavbarActions';
 
+// 布局配置
+import { LAYOUT_PADDING } from '../../layouts/config/layoutConfig';
+
 // Phase 4: MoreNavMenu 和 NavItems 组件已提取到 Navigation 目录
 
 export default function HomeNavbar() {
@@ -150,7 +153,7 @@ export default function HomeNavbar() {
                 borderColor={navbarBorder}
                 py={{ base: 2, md: 3 }}
             >
-                <Box px={{ base: 4, md: 6, lg: '80px' }}>
+                <Box px={LAYOUT_PADDING.x}>
                     <Flex justify="space-between" align="center">
                         {/* Logo - 价小前投研 */}
                         <BrandLogo />