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/artifacts/artifact-file-detail.tsx

@@ -32,13 +32,11 @@ import {
 import { ToggleGroup, ToggleGroupItem } from "@/components/ui/toggle-group";
 import { CodeEditor } from "@/components/workspace/code-editor";
 import { useArtifactContent } from "@/core/artifacts/hooks";
-import { CitationsLoadingIndicator } from "@/components/ai-elements/inline-citation";
 import { urlOfArtifact } from "@/core/artifacts/utils";
 import type { Citation } from "@/core/citations";
 import {
   contentWithoutCitationsFromParsed,
   removeAllCitations,
-  shouldShowCitationLoading,
   useParsedCitations,
 } from "@/core/citations";
 import { useI18n } from "@/core/i18n/hooks";
@@ -50,6 +48,7 @@ import { cn } from "@/lib/utils";
 
 import { Tooltip } from "../tooltip";
 
+import { SafeCitationContent } from "../messages/safe-citation-content";
 import { useThread } from "../messages/context";
 
 import { useArtifacts } from "./context";
@@ -252,31 +251,27 @@ export function ArtifactFileDetail({
         </div>
       </ArtifactHeader>
       <ArtifactContent className="p-0">
-        {previewable && viewMode === "preview" && (
+        {previewable &&
+          viewMode === "preview" &&
           language === "markdown" &&
-          content &&
-          shouldShowCitationLoading(
-            content,
-            parsed.cleanContent,
-            thread.isLoading,
-          ) ? (
-            <div className="flex size-full items-center justify-center p-4">
-              <CitationsLoadingIndicator
-                citations={parsed.citations}
-                className="my-0"
-              />
-            </div>
-          ) : (
-            <ArtifactFilePreview
-              filepath={filepath}
-              threadId={threadId}
+          content && (
+            <SafeCitationContent
               content={content}
-              language={language ?? "text"}
-              cleanContent={parsed.cleanContent}
-              citationMap={parsed.citationMap}
+              isLoading={thread.isLoading}
+              rehypePlugins={streamdownPlugins.rehypePlugins}
+              className="flex size-full items-center justify-center p-4 my-0"
+              renderBody={(p) => (
+                <ArtifactFilePreview
+                  filepath={filepath}
+                  threadId={threadId}
+                  content={content}
+                  language={language ?? "text"}
+                  cleanContent={p.cleanContent}
+                  citationMap={p.citationMap}
+                />
+              )}
             />
-          )
-        )}
+          )}
         {isCodeFile && viewMode === "code" && (
           <CodeEditor
             className="size-full resize-none rounded-none border-none"