feat: add forum seed categories, improve page layouts and navigation

- Seed default forum categories (announcements, learning, feedback) on startup
- Update forum pages with improved category/post/reply UI
- Refine navbar, mobile nav, and home page content layout
- Improve analytics, course-content, knowledge, profile, settings, spatial pages

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

web/src/app/(main)/spatial/page.tsx

@@ -375,12 +375,6 @@ export default function SpatialPage() {
   return (
     <div className="min-h-screen bg-background">
       <div className="max-w-7xl mx-auto px-4 sm:px-6 lg:px-8 py-8">
-        {/* 页面头部 */}
-        <div className="mb-8">
-          <h1 className="text-3xl font-bold text-foreground mb-2">空间出图</h1>
-          <p className="text-muted-foreground">使用AI生成国土空间规划相关的设计图和示意图</p>
-        </div>
-
         {/* Tab导航 */}
         <Tabs defaultValue="text-to-image" className="w-full">
           <TabsList className="grid w-full grid-cols-2">