refactor(layout): 统一页面边距管理，移除 Container 限制

- layoutConfig.js: 新增 LAYOUT_PADDING 常量 { base: 4, md: 6, lg: '80px' }
- MainLayout.js: 在 Outlet 容器上统一应用 px={LAYOUT_PADDING.x}
- HomeNavbar.js: 边距从 lg:8 改为 lg:'80px'，与内容区对齐
- AppFooter.js: 移除 Container，边距改为 lg:'80px'

页面组件清理（移除冗余的 px/Container）：
- Company, Community, Center, Profile, Settings
- ValueForum, DataBrowser, LimitAnalyse, StockOverview, Concept

特殊处理：
- CompanyHeader: 使用负边距实现全宽背景
- Concept Hero: 使用负边距实现全宽背景

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

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

src/views/ValueForum/PostDetail.js

@@ -6,7 +6,6 @@
 import React, { useState, useEffect } from 'react';
 import {
   Box,
-  Container,
   Heading,
   Text,
   HStack,
@@ -157,7 +156,6 @@ const PostDetail = () => {
 
   return (
     <Box minH="100vh" bg={forumColors.background.main} pt="80px" pb="20">
-      <Container maxW="container.xl">
         {/* 返回按钮 */}
         <Button
           leftIcon={<ArrowLeft size={18} />}
@@ -374,7 +372,6 @@ const PostDetail = () => {
             </MotionBox>
           </Box>
         </SimpleGrid>
-      </Container>
 
       {/* 图片预览弹窗 */}
       <ImagePreviewModal

src/views/ValueForum/PredictionTopicDetail.js

@@ -6,7 +6,6 @@
 import React, { useState, useEffect } from 'react';
 import {
   Box,
-  Container,
   Heading,
   Text,
   Button,
@@ -224,7 +223,6 @@ const PredictionTopicDetail = () => {
 
   return (
     <Box minH="100vh" bg={forumColors.background.main} pt={LAYOUT_SIZE.navbarHeight} pb={{ base: "6", md: "20" }}>
-      <Container maxW="container.xl" px={{ base: "3", sm: "4", md: "6" }}>
         {/* 头部：返回按钮 */}
         <Button
           variant="ghost"
@@ -627,7 +625,6 @@ const PredictionTopicDetail = () => {
             </MotionBox>
           </Box>
         </SimpleGrid>
-      </Container>
 
       {/* 交易模态框 */}
       <TradeModal

src/views/ValueForum/index.js

@@ -6,7 +6,6 @@
 import React, { useState, useEffect } from 'react';
 import {
   Box,
-  Container,
   Heading,
   Text,
   Button,
@@ -154,7 +153,8 @@ const ValueForum = () => {
       pt="80px"
       pb="20"
     >
-      <Container maxW="container.xl">
+      {/* padding 由 MainLayout 统一设置 */}
+      <Box>
         {/* 顶部横幅 */}
         <MotionBox
           initial={{ opacity: 0, y: -20 }}
@@ -469,7 +469,7 @@ const ValueForum = () => {
             </TabPanel>
           </TabPanels>
         </Tabs>
-      </Container>
+      </Box>
 
       {/* 发帖模态框 */}
       <CreatePostModal