chore: 移除所有 Citations 相关逻辑，为后续重构做准备

- Backend: 删除 lead_agent / general_purpose 中的 citations_format 与引用相关 reminder；artifacts 下载不再对 markdown 做 citation 清洗，统一走 FileResponse，保留 Response 用于二进制 inline
- Frontend: 删除 core/citations 模块、inline-citation、safe-citation-content；新增 MarkdownContent 仅做 Markdown 渲染；消息/artifact 预览与复制均使用原始 content
- i18n: 移除 citations 命名空间（loadingCitations、loadingCitationsWithCount）
- 技能与 demo: 措辞改为 references，demo 数据去掉 <citations> 块
- 文档: 更新 CLAUDE/AGENTS/README 描述，新增按文件 diff 的代码变更总结

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

backend/src/agents/lead_agent/prompt.py

@@ -240,34 +240,8 @@ You have access to skills that provide optimized workflows for specific tasks. E
 - Action-Oriented: Focus on delivering results, not explaining processes
 </response_style>
 
-<citations_format>
-After web_search, ALWAYS include citations in your output:
-
-1. Start with a `<citations>` block in JSONL format listing all sources
-2. In content, use FULL markdown link format: [Short Title](full_url)
-
-**CRITICAL - Citation Link Format:**
-- CORRECT: `[TechCrunch](https://techcrunch.com/ai-trends)` - full markdown link with URL
-- WRONG: `[arXiv:2502.19166]` - missing URL, will NOT render as link
-- WRONG: `[Source]` - missing URL, will NOT render as link
-
-**Rules:**
-- Every citation MUST be a complete markdown link with URL: `[Title](https://...)`
-- Write content naturally, add citation link at end of sentence/paragraph
-- NEVER use bare brackets like `[arXiv:xxx]` or `[Source]` without URL
-
-**Example:**
-<citations>
-{{"id": "cite-1", "title": "AI Trends 2026", "url": "https://techcrunch.com/ai-trends", "snippet": "Tech industry predictions"}}
-{{"id": "cite-2", "title": "OpenAI Research", "url": "https://openai.com/research", "snippet": "Latest AI research developments"}}
-</citations>
-The key AI trends for 2026 include enhanced reasoning capabilities and multimodal integration [TechCrunch](https://techcrunch.com/ai-trends). Recent breakthroughs in language models have also accelerated progress [OpenAI](https://openai.com/research).
-</citations_format>
-
-
 <critical_reminders>
 - **Clarification First**: ALWAYS clarify unclear/missing/ambiguous requirements BEFORE starting work - never assume or guess
-- **Web search citations**: When you use web_search (or synthesize subagent results that used it), you MUST output the `<citations>` block and [Title](url) links as specified in citations_format so citations display for the user.
 {subagent_reminder}- Skill First: Always load the relevant skill before starting **complex** tasks.
 - Progressive Loading: Load resources incrementally as referenced in skills
 - Output Files: Final deliverables must be in `/mnt/user-data/outputs`
@@ -341,7 +315,6 @@ def apply_prompt_template(subagent_enabled: bool = False) -> str:
     # Add subagent reminder to critical_reminders if enabled
     subagent_reminder = (
         "- **Orchestrator Mode**: You are a task orchestrator - decompose complex tasks into parallel sub-tasks and launch multiple subagents simultaneously. Synthesize results, don't execute directly.\n"
-        "- **Citations when synthesizing**: When you synthesize subagent results that used web search or cite sources, you MUST include a consolidated `<citations>` block (JSONL format) and use [Title](url) markdown links in your response so citations display correctly.\n"
         if subagent_enabled
         else ""
     )