feat(frontend): unify citation logic and prevent half-finished citations

- Add SafeCitationContent as single component for citation-aware body:
  useParsedCitations + shouldShowCitationLoading; show loading until
  citations complete, then render body with createCitationMarkdownComponents.
  Supports optional remarkPlugins, rehypePlugins, isHuman, img.

- Refactor MessageListItem: assistant message body now uses
  SafeCitationContent only; remove duplicate useParsedCitations,
  shouldShowCitationLoading, createCitationMarkdownComponents and
  CitationsLoadingIndicator logic. Human messages keep plain
  AIElementMessageResponse (no citation parsing).

- Use SafeCitationContent for clarification, present-files (message-list),
  thinking steps and write_file loading (message-group), subtask result
  (subtask-card). Artifact markdown preview keeps same guard
  (shouldShowCitationLoading) with ArtifactFilePreview.

- Unify loading condition: shouldShowCitationLoading(rawContent,
  cleanContent, isLoading) is the single source of truth. Show loading when
  (isLoading && hasCitationsBlock(rawContent)) or when
  (hasCitationsBlock(rawContent) && hasUnreplacedCitationRefs(cleanContent))
  so Pro/Ultra modes also show "loading citations" and half-finished
  [cite-N] never appear.

- message-group write_file: replace hasCitationsBlock + threadIsLoading
  with shouldShowCitationLoading(fileContent, cleanContent,
  threadIsLoading && isLast) for consistency.

- citations/utils: parse incomplete <citations> during streaming;
  remove isCitationsBlockIncomplete; keep hasUnreplacedCitationRefs
  internal; document display rule in file header.

Co-authored-by: Cursor <cursoragent@cursor.com>

---
feat(前端): 统一引用逻辑并杜绝半成品引用

- 新增 SafeCitationContent 作为引用正文的唯一出口：内部使用
  useParsedCitations + shouldShowCitationLoading，在引用未就绪时只显示
  「正在整理引用」，就绪后用 createCitationMarkdownComponents 渲染正文；
  支持可选 remarkPlugins、rehypePlugins、isHuman、img。

- 重构 MessageListItem：助手消息正文仅通过 SafeCitationContent 渲染，
  删除重复的 useParsedCitations、shouldShowCitationLoading、
  createCitationMarkdownComponents、CitationsLoadingIndicator 等逻辑；
  用户消息仍用 AIElementMessageResponse，不做引用解析。

- 澄清、present-files（message-list）、思考步骤与 write_file 加载
  （message-group）、子任务结果（subtask-card）均使用
  SafeCitationContent；Artifact 的 markdown 预览仍用同一 guard
  shouldShowCitationLoading，正文由 ArtifactFilePreview 渲染。

- 统一加载条件：shouldShowCitationLoading(rawContent, cleanContent,
  isLoading) 为唯一判断。在「流式中且已有引用块」或「有引用块且
  cleanContent 中仍有未替换的 [cite-N]」时仅显示加载，从而在 Pro/Ultra
  下也能看到「正在整理引用」，且永不出现半成品 [cite-N]。

- message-group 的 write_file：用 shouldShowCitationLoading(
  fileContent, cleanContent, threadIsLoading && isLast) 替代
  hasCitationsBlock + threadIsLoading，与其他场景一致。

- citations/utils：流式时解析未闭合的 <citations>；移除
  isCitationsBlockIncomplete；hasUnreplacedCitationRefs 保持内部使用；
  在文件头注释中说明展示规则。

frontend/src/components/ai-elements/inline-citation.tsx

@@ -12,7 +12,14 @@ import {
   externalLinkClassNoUnderline,
 } from "@/lib/utils";
 import { ExternalLinkIcon } from "lucide-react";
-import { type ComponentProps, Children } from "react";
+import {
+  type AnchorHTMLAttributes,
+  type ComponentProps,
+  type ImgHTMLAttributes,
+  type ReactElement,
+  type ReactNode,
+  Children,
+} from "react";
 import type { Citation } from "@/core/citations";
 import {
   extractDomainFromUrl,
@@ -202,6 +209,48 @@ export const CitationAwareLink = ({
   );
 };
 
+/**
+ * Options for creating markdown components that render links as citations.
+ * Used by message list (all modes: Flash/Thinking/Pro/Ultra), artifact preview, and CoT.
+ */
+export type CreateCitationMarkdownComponentsOptions = {
+  citationMap: Map<string, Citation>;
+  isHuman?: boolean;
+  isLoadingCitations?: boolean;
+  syntheticExternal?: boolean;
+  /** Optional custom img component (e.g. MessageImage with threadId). Omit for artifact. */
+  img?: (props: ImgHTMLAttributes<HTMLImageElement> & { threadId?: string; maxWidth?: string }) => ReactNode;
+};
+
+/**
+ * Create markdown `components` (a, optional img) that use CitationAwareLink.
+ * Reused across message-list-item (all modes), artifact-file-detail, and any CoT markdown.
+ */
+export function createCitationMarkdownComponents(
+  options: CreateCitationMarkdownComponentsOptions,
+): {
+  a: (props: AnchorHTMLAttributes<HTMLAnchorElement>) => ReactElement;
+  img?: (props: ImgHTMLAttributes<HTMLImageElement> & { threadId?: string; maxWidth?: string }) => ReactNode;
+} {
+  const {
+    citationMap,
+    isHuman = false,
+    isLoadingCitations = false,
+    syntheticExternal = false,
+    img,
+  } = options;
+  const a = (props: AnchorHTMLAttributes<HTMLAnchorElement>) => (
+    <CitationAwareLink
+      {...props}
+      citationMap={citationMap}
+      isHuman={isHuman}
+      isLoadingCitations={isLoadingCitations}
+      syntheticExternal={syntheticExternal}
+    />
+  );
+  return img ? { a, img } : { a };
+}
+
 /**
  * Shared CitationsLoadingIndicator component
  * Used across message-list-item and message-group to show loading citations