refactor: overhaul homepage and app structure

Simplify homepage, show chapter counts, display directory, trim bottom nav, in-page match feature, move marketing content, and enhance "My" page.

#VERCEL_SKIP

Co-authored-by: undefined <undefined+undefined@users.noreply.github.com>

开发文档/6、后端/后端开发规范.md

@@ -45,7 +45,7 @@
 3.  **逻辑图解**：用 Mermaid 展示异步处理流程。
 
 ### 示例 Mermaid (类图)
-```mermaid
+\`\`\`mermaid
 classDiagram
     class UserRouter {
         +get_user()
@@ -61,4 +61,4 @@ classDiagram
     }
     UserRouter --> UserService
     UserService --> VectorStore
-```
+\`\`\`