feat(citations): inline citation links with [citation:Title](URL)

- Backend: add citation format to lead_agent and general_purpose prompts
- Add CitationLink component (Badge + HoverCard) for citation cards
- MarkdownContent: detect citation: prefix in link text, render CitationLink
- Message/artifact/subtask: use MarkdownContent or Streamdown with CitationLink
- message-list-item: pass img via components prop (remove isHuman/img)
- message-group, subtask-card: drop unused imports; fix import order (lint)

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

frontend/src/app/workspace/chats/[thread_id]/page.tsx

@@ -1,5 +1,6 @@
 "use client";
 
+import type { Message } from "@langchain/langgraph-sdk";
 import { FilesIcon, XIcon } from "lucide-react";
 import { useParams, useRouter, useSearchParams } from "next/navigation";
 import { useCallback, useEffect, useMemo, useState } from "react";
@@ -30,7 +31,6 @@ import { useNotification } from "@/core/notification/hooks";
 import { useLocalSettings } from "@/core/settings";
 import { type AgentThread, type AgentThreadState } from "@/core/threads";
 import { useSubmitThread, useThreadStream } from "@/core/threads/hooks";
-import type { Message } from "@langchain/langgraph-sdk";
 import {
   pathOfThread,
   textOfMessage,