feat: add inline citations and thread management features

Citations:
- Add citations parsing utilities for extracting source references from AI responses
- Render inline citations as hover card badges in message content
- Display citation cards with title, URL, and description on hover
- Add citation badge rendering in artifact markdown preview
- Update prompt to guide AI to output citations in correct format

Thread Management:
- Add rename functionality for chat threads with dialog UI
- Add share functionality to copy thread link to clipboard
- Share links use Vercel URL for production accessibility
- Add useRenameThread hook for thread title updates

i18n:
- Add translations for rename, share, cancel, save, and linkCopied

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

frontend/src/core/citations/index.ts

@@ -0,0 +1,8 @@
+export {
+  parseCitations,
+  buildCitationMap,
+  extractDomainFromUrl,
+  isCitationsBlockIncomplete,
+} from "./utils";
+
+export type { Citation, ParseCitationsResult } from "./utils";

frontend/src/core/citations/utils.ts

@@ -0,0 +1,124 @@
+/**
+ * Citation data structure representing a source reference
+ */
+export interface Citation {
+  id: string;
+  title: string;
+  url: string;
+  snippet: string;
+}
+
+/**
+ * Result of parsing citations from content
+ */
+export interface ParseCitationsResult {
+  citations: Citation[];
+  cleanContent: string;
+}
+
+/**
+ * Parse citations block from message content.
+ *
+ * The citations block format:
+ * <citations>
+ * {"id": "cite-1", "title": "Page Title", "url": "https://example.com", "snippet": "Description"}
+ * {"id": "cite-2", "title": "Another Page", "url": "https://example2.com", "snippet": "Description"}
+ * </citations>
+ *
+ * @param content - The raw message content that may contain a citations block
+ * @returns Object containing parsed citations array and content with citations block removed
+ */
+export function parseCitations(content: string): ParseCitationsResult {
+  if (!content) {
+    return { citations: [], cleanContent: content };
+  }
+
+  // Match the citations block at the start of content (with possible leading whitespace)
+  const citationsRegex = /^\s*<citations>([\s\S]*?)<\/citations>/;
+  const match = citationsRegex.exec(content);
+
+  if (!match) {
+    return { citations: [], cleanContent: content };
+  }
+
+  const citationsBlock = match[1] ?? "";
+  const citations: Citation[] = [];
+
+  // Parse each line as JSON
+  const lines = citationsBlock.split("\n");
+  for (const line of lines) {
+    const trimmed = line.trim();
+    if (trimmed?.startsWith("{")) {
+      try {
+        const citation = JSON.parse(trimmed) as Citation;
+        // Validate required fields
+        if (citation.id && citation.url) {
+          citations.push({
+            id: citation.id,
+            title: citation.title || "",
+            url: citation.url,
+            snippet: citation.snippet || "",
+          });
+        }
+      } catch {
+        // Skip invalid JSON lines - this can happen during streaming
+      }
+    }
+  }
+
+  // Remove the citations block from content
+  const cleanContent = content.replace(citationsRegex, "").trim();
+
+  return { citations, cleanContent };
+}
+
+/**
+ * Build a map from URL to Citation for quick lookup
+ *
+ * @param citations - Array of citations
+ * @returns Map with URL as key and Citation as value
+ */
+export function buildCitationMap(
+  citations: Citation[],
+): Map<string, Citation> {
+  const map = new Map<string, Citation>();
+  for (const citation of citations) {
+    map.set(citation.url, citation);
+  }
+  return map;
+}
+
+/**
+ * Extract the domain name from a URL for display
+ *
+ * @param url - Full URL string
+ * @returns Domain name or the original URL if parsing fails
+ */
+export function extractDomainFromUrl(url: string): string {
+  try {
+    const urlObj = new URL(url);
+    // Remove 'www.' prefix if present
+    return urlObj.hostname.replace(/^www\./, "");
+  } catch {
+    return url;
+  }
+}
+
+/**
+ * Check if content is still receiving the citations block (streaming)
+ * This helps determine if we should wait before parsing
+ *
+ * @param content - The current content being streamed
+ * @returns true if citations block appears to be incomplete
+ */
+export function isCitationsBlockIncomplete(content: string): boolean {
+  if (!content) {
+    return false;
+  }
+
+  // Check if we have an opening tag but no closing tag
+  const hasOpenTag = content.includes("<citations>");
+  const hasCloseTag = content.includes("</citations>");
+
+  return hasOpenTag && !hasCloseTag;
+}