refactor(frontend): simplify and deduplicate Citation-related code

- Extract removeCitationsBlocks in utils, reuse in parseCitations and removeAllCitations
- Add hasCitationsBlock; isCitationsBlockIncomplete now uses it
- Add useParsedCitations hook (parseCitations + buildCitationMap) for message/artifact
- Add CitationAwareLink to unify link rendering (message-list-item + artifact-file-detail)
- Add getCleanContent helper; message-group uses it and useParsedCitations
- ArtifactFileDetail: single useParsedCitations, pass cleanContent/citationMap to Preview
- Stop exporting buildCitationMap and removeCitationsBlocks from citations index
- Remove duplicate MessageLink and inline link logic in artifact preview

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

frontend/src/core/citations/use-parsed-citations.ts

@@ -0,0 +1,28 @@
+"use client";
+
+import { useMemo } from "react";
+
+import { buildCitationMap, parseCitations } from "./utils";
+import type { Citation } from "./utils";
+
+export interface UseParsedCitationsResult {
+  citations: Citation[];
+  cleanContent: string;
+  citationMap: Map<string, Citation>;
+}
+
+/**
+ * Parse content for citations and build citation map. Memoized by content.
+ * Use in message and artifact components to avoid repeating parseCitations + buildCitationMap.
+ */
+export function useParsedCitations(content: string): UseParsedCitationsResult {
+  return useMemo(() => {
+    const parsed = parseCitations(content ?? "");
+    const citationMap = buildCitationMap(parsed.citations);
+    return {
+      citations: parsed.citations,
+      cleanContent: parsed.cleanContent,
+      citationMap,
+    };
+  }, [content]);
+}