feat: add cover image functionality for articles

- Implemented `resolveApiURL` function to handle various URL formats.
- Updated `ArticleDetail` and `UpdateArticleRequest` interfaces to include `cover_asset_url`.
- Enhanced `ArticleEditorView` to manage cover image uploads, including a new `CoverPickerModal` component.
- Added cover image requirements logic in `cover-requirements.ts` to enforce platform-specific cover image rules.
- Modified backend services to handle cover image uploads and validations, including checks for required cover images for specific platforms.
- Improved error handling for cover image requirements during article publishing.

packages/shared-types/src/index.ts

@@ -254,6 +254,7 @@ export interface ArticleDetail {
   template_name: string | null;
   generation_mode: string | null;
   platforms: string[];
+  cover_asset_url: string | null;
   generate_status: string;
   publish_status: string;
   title: string | null;
@@ -275,6 +276,7 @@ export interface UpdateArticleRequest {
   title: string;
   markdown_content: string;
   platforms?: string[];
+  cover_asset_url?: string | null;
 }
 
 export interface ArticleImageUploadResponse {