feat(admin-web): add paste-text source mode to imitation create page

- Add a source-method toggle (article URL / pasted text) with per-mode
  hints, a 24,000-character counter, and mode-aware submit validation
- Validate URLs client-side (http/https only) with a dedicated error
  message; only the active mode's field is sent to the API
- Keep URL mode selected when arriving with source_url query params
- Refresh the page layout and update zh-CN/en-US copy for both modes

apps/admin-web/src/i18n/messages/en-US.ts

@@ -224,7 +224,7 @@ const enUS = {
     },
     imitationCreate: {
       title: 'Imitation Create',
-      description: 'Extract an article from a URL, then generate a new article in one step.',
+      description: 'Extract from an article URL first, or paste the source text directly.',
     },
     media: {
       title: 'Media Management',
@@ -854,10 +854,18 @@ const enUS = {
     create: {
       title: 'Create rewritten article',
       subtitle:
-        'The backend fetches the source article first, then generates a new original article from your settings.',
+        'Extract from an article URL or paste the source text to generate a new article for the current brand.',
       sourceSection: 'Source article',
       settingsSection: 'Rewrite settings',
+      settingsHint: 'Set the brand context, reference sources, and writing constraints.',
+      sourceMethod: 'Source method',
+      sourcePriority: 'URL is recommended',
+      sourceURLMode: 'Article URL',
+      sourceContentMode: 'Paste text',
+      sourceURLModeHint: 'The page title and article body will be extracted automatically.',
+      sourceContentModeHint: 'Use text from restricted pages or an existing document.',
       sourceURL: 'Article URL',
+      sourceContent: 'Source text',
       sourceTitle: 'Source title',
       language: 'Article language',
       brandName: 'Current company',
@@ -874,6 +882,9 @@ const enUS = {
       knowledgeBaseHint:
         'Selected groups are retrieved in the backend and passed to generation as reference context.',
       sourceURLPlaceholder: 'https://example.com/article',
+      sourceContentPlaceholder:
+        'Paste the complete source article here, including relevant headings and data.',
+      sourceContentCount: '{count} / 24,000 characters',
       sourceTitlePlaceholder: 'Optional. Citation titles are prefilled automatically.',
       brandNamePlaceholder: 'Select the current company in the top bar first.',
       regionPlaceholder: 'For example: Shanghai, East China, nationwide, North America',
@@ -885,6 +896,8 @@ const enUS = {
         'Add channel, structure, title style, or industry-specific instructions.',
       queued: 'Rewrite task submitted and queued.',
       sourceURLRequired: 'Enter the source article URL first.',
+      sourceURLInvalid: 'Enter a valid link beginning with http:// or https://.',
+      sourceContentRequired: 'Paste the source article text first.',
       brandNameRequired: 'Select the current company in the top bar first.',
       submitError: 'Failed to submit rewrite task.',
       backToList: 'Back to rewrites',

apps/admin-web/src/i18n/messages/zh-CN.ts

@@ -228,7 +228,7 @@ const zhCN = {
     },
     imitationCreate: {
       title: '仿写创作',
-      description: '从文章链接提取内容后，一步生成适配当前场景的新文章。',
+      description: '优先从文章链接提取内容，也可直接粘贴正文作为仿写来源。',
     },
     media: {
       title: '媒体管理',
@@ -831,10 +831,18 @@ const zhCN = {
     },
     create: {
       title: '创建仿写文章',
-      subtitle: '后台会先抓取源文章内容，再按下方设定生成一篇新的原创表达文章。',
+      subtitle: '从文章 URL 自动提取，或粘贴正文，生成符合当前品牌场景的新文章。',
       sourceSection: '来源文章',
       settingsSection: '仿写设置',
+      settingsHint: '设置品牌、增强信息与表达边界，未填写项将使用默认生成策略。',
+      sourceMethod: '来源方式',
+      sourcePriority: '推荐优先使用 URL',
+      sourceURLMode: '文章 URL',
+      sourceContentMode: '粘贴正文',
+      sourceURLModeHint: '系统将自动解析网页中的标题与正文内容',
+      sourceContentModeHint: '适用于无法直接访问的网页或已有文档内容',
       sourceURL: '文章 URL',
+      sourceContent: '原文正文',
       sourceTitle: '来源标题',
       language: '文章语言',
       brandName: '当前公司',
@@ -850,6 +858,8 @@ const zhCN = {
       knowledgeBaseHint:
         '选择后，后台会检索相关知识片段并作为生成参考，未选择则只基于来源文章和当前设置生成。',
       sourceURLPlaceholder: 'https://example.com/article',
+      sourceContentPlaceholder: '在此粘贴完整原文，保留必要的标题、段落与数据即可',
+      sourceContentCount: '已输入 {count} / 24,000 字',
       sourceTitlePlaceholder: '可选，引用来源标题会自动带入',
       brandNamePlaceholder: '请先在顶部选择当前公司',
       regionPlaceholder: '例如：上海、华东、全国、北美市场',
@@ -859,6 +869,8 @@ const zhCN = {
       extraRequirementsPlaceholder: '补充行业、渠道、结构、标题风格等自由要求',
       queued: '仿写任务已提交，正在排队生成',
       sourceURLRequired: '请先填写来源文章 URL',
+      sourceURLInvalid: '请输入以 http:// 或 https:// 开头的有效链接',
+      sourceContentRequired: '请先粘贴需要仿写的原文正文',
       brandNameRequired: '请先在顶部选择当前公司',
       submitError: '仿写任务提交失败',
       backToList: '返回仿写列表',