refactor(frontend): consolidate citation logic, slim exports and impl

- SafeCitationContent: add loadingOnly and renderBody props.
  - loadingOnly: show only loading indicator or null (e.g. write_file step).
  - renderBody(parsed): custom body renderer (e.g. artifact preview).

- message-group write_file: use SafeCitationContent(content, isLoading,
  rehypePlugins, loadingOnly) instead of local useParsedCitations +
  shouldShowCitationLoading + CitationsLoadingIndicator. Pass rehypePlugins
  into ToolCall.

- artifact-file-detail markdown preview: use SafeCitationContent with
  renderBody((p) => <ArtifactFilePreview ... cleanContent={p.cleanContent}
  citationMap={p.citationMap} />). Remove local shouldShowCitationLoading
  and CitationsLoadingIndicator branch.

- core/citations: inline buildCitationMap into use-parsed-citations, remove
  from utils; stop exporting hasCitationsBlock (internal to shouldShowCitationLoading).

- inline-citation: make InlineCitationCard, InlineCitationCardBody,
  InlineCitationSource file-private (no longer exported).

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

---
refactor(前端): 收拢引用逻辑、精简导出与实现

- SafeCitationContent 新增 loadingOnly、renderBody。
  - loadingOnly：仅显示加载或 null（如 write_file 步骤）。
  - renderBody(parsed)：自定义正文渲染（如 artifact 预览）。

- message-group write_file：改用 SafeCitationContent(loadingOnly)，去掉
  本地 useParsedCitations + shouldShowCitationLoading + CitationsLoadingIndicator，
  并向 ToolCall 传入 rehypePlugins。

- artifact-file-detail 的 markdown 预览：改用 SafeCitationContent +
  renderBody 渲染 ArtifactFilePreview，去掉本地加载判断与
  CitationsLoadingIndicator 分支。

- core/citations：buildCitationMap 内联到 use-parsed-citations 并从 utils
  删除；hasCitationsBlock 不再导出（仅 shouldShowCitationLoading 内部使用）。

- inline-citation：InlineCitationCard/Body/Source 改为文件内私有，不再导出。

frontend/src/components/workspace/messages/safe-citation-content.tsx

@@ -1,6 +1,7 @@
 "use client";
 
 import type { ImgHTMLAttributes } from "react";
+import type { ReactNode } from "react";
 import { useMemo } from "react";
 
 import {
@@ -14,6 +15,7 @@ import {
 import {
   shouldShowCitationLoading,
   useParsedCitations,
+  type UseParsedCitationsResult,
 } from "@/core/citations";
 import { streamdownPlugins } from "@/core/streamdown";
 import { cn } from "@/lib/utils";
@@ -25,7 +27,11 @@ export type SafeCitationContentProps = {
   className?: string;
   remarkPlugins?: MessageResponseProps["remarkPlugins"];
   isHuman?: boolean;
-  img?: (props: ImgHTMLAttributes<HTMLImageElement> & { threadId?: string; maxWidth?: string }) => React.ReactNode;
+  img?: (props: ImgHTMLAttributes<HTMLImageElement> & { threadId?: string; maxWidth?: string }) => ReactNode;
+  /** When true, only show loading indicator or null (e.g. write_file step). */
+  loadingOnly?: boolean;
+  /** When set, use instead of default MessageResponse (e.g. artifact preview). */
+  renderBody?: (parsed: UseParsedCitationsResult) => ReactNode;
 };
 
 /** Single place for citation-aware body: shows loading until citations complete (no half-finished refs), else body. */
@@ -37,20 +43,12 @@ export function SafeCitationContent({
   remarkPlugins = streamdownPlugins.remarkPlugins,
   isHuman = false,
   img,
+  loadingOnly = false,
+  renderBody,
 }: SafeCitationContentProps) {
-  const { citations, cleanContent, citationMap } = useParsedCitations(content);
+  const parsed = useParsedCitations(content);
+  const { citations, cleanContent, citationMap } = parsed;
   const showLoading = shouldShowCitationLoading(content, cleanContent, isLoading);
-
-  if (showLoading) {
-    return (
-      <CitationsLoadingIndicator
-        citations={citations}
-        className={cn("my-2", className)}
-      />
-    );
-  }
-  if (!cleanContent) return null;
-
   const components = useMemo(
     () =>
       createCitationMarkdownComponents({
@@ -61,6 +59,19 @@ export function SafeCitationContent({
       }),
     [citationMap, isHuman, img],
   );
+
+  if (showLoading) {
+    return (
+      <CitationsLoadingIndicator
+        citations={citations}
+        className={cn("my-2", className)}
+      />
+    );
+  }
+  if (loadingOnly) return null;
+  if (renderBody) return renderBody(parsed);
+  if (!cleanContent) return null;
+
   return (
     <MessageResponse
       className={className}