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/i18n/locales/en-US.ts

@@ -11,6 +11,8 @@ export const enUS: Translations = {
     home: "Home",
     settings: "Settings",
     delete: "Delete",
+    rename: "Rename",
+    share: "Share",
     openInNewWindow: "Open in new window",
     close: "Close",
     more: "More",
@@ -24,6 +26,8 @@ export const enUS: Translations = {
     loading: "Loading...",
     code: "Code",
     preview: "Preview",
+    cancel: "Cancel",
+    save: "Save",
   },
 
   // Welcome
@@ -38,6 +42,7 @@ export const enUS: Translations = {
     copyToClipboard: "Copy to clipboard",
     copiedToClipboard: "Copied to clipboard",
     failedToCopyToClipboard: "Failed to copy to clipboard",
+    linkCopied: "Link copied to clipboard",
   },
 
   // Input Box