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/components/workspace/messages/message-group.tsx

@@ -22,7 +22,6 @@ import {
   ChainOfThoughtStep,
 } from "@/components/ai-elements/chain-of-thought";
 import { CodeBlock } from "@/components/ai-elements/code-block";
-import { MessageResponse } from "@/components/ai-elements/message";
 import { Button } from "@/components/ui/button";
 import { useI18n } from "@/core/i18n/hooks";
 import {
@@ -30,7 +29,6 @@ import {
   findToolCallResult,
 } from "@/core/messages/utils";
 import { useRehypeSplitWordsIntoSpans } from "@/core/rehype";
-import { streamdownPlugins } from "@/core/streamdown";
 import { extractTitleFromMarkdown } from "@/core/utils/markdown";
 import { env } from "@/env";
 import { cn } from "@/lib/utils";