feat(imitation): add article imitation create flow

Introduce 仿写创作: new list and create views, backend imitation service
and prompt templates, worker task routing for imitation jobs, and one-click
rewrite triggers from question citation sources. Surface source article
URL/title on article list/detail, and restrict failed articles to delete-only.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/shared-types/src/index.ts

@@ -502,6 +502,8 @@ export interface ArticleListItem {
   generation_error_message: string | null;
   word_count: number;
   source_label: string | null;
+  source_url?: string | null;
+  source_title?: string | null;
   created_at: string;
 }
 
@@ -528,6 +530,8 @@ export interface ArticleDetail {
   markdown_content: string | null;
   word_count: number;
   source_label: string | null;
+  source_url?: string | null;
+  source_title?: string | null;
   version_no: number | null;
   generation_error_message: string | null;
   wizard_state?: Record<string, JsonValue> | null;
@@ -538,6 +542,31 @@ export interface CreateArticleRequest {
   title?: string;
 }
 
+export interface GenerateImitationRequest {
+  source_url: string;
+  source_title?: string;
+  locale?: string;
+  industry?: string;
+  brand_name?: string;
+  region?: string;
+  target_audience?: string;
+  content_goal?: string;
+  tone?: string;
+  length_goal?: string;
+  keywords?: string[];
+  preserve_points?: string;
+  avoid_points?: string;
+  extra_requirements?: string;
+  enable_web_search?: boolean;
+  web_search_limit?: number;
+  knowledge_group_ids?: number[];
+}
+
+export interface GenerateImitationResponse {
+  article_id: number;
+  task_id: number;
+}
+
 export interface UpdateArticleRequest {
   title: string;
   markdown_content: string;