feat: add citation/reference support to deep research reports (#1143)

* feat: add citation/reference support to deep research reports (#1141)

- Enhance lead agent system prompt with mandatory citation requirements
  after web_search/web_fetch tool usage
- Add citation examples and best practices to GitHub Deep Research skill
- Add citation hints to report template (Executive Summary, Key Analysis)
- Style regular markdown links in frontend for visual distinction
  (color, underline, hover effect)
- Fix TitleMiddleware being registered when title generation is disabled

* fix: address PR review comments

- Revert TitleMiddleware conditional registration (agent.py) to avoid
  sync/async incompatibility with DeerFlowClient
- Fix markdown link rendering: merge classNames instead of overwriting,
  only set target=_blank for external http(s) URLs
- Remove unrelated package.json/pnpm-lock.yaml changes

* fix: use plain markdown links in Sources section for cleaner rendering

Inline citations in report body use [citation:Title](URL) for pill/badge style.
Sources section uses plain [Title](URL) for simple underlined link style.

* fix(frontend): render plain links as underlined text in artifact markdown

Only links with citation: prefix render as Badge pills.
Regular links in Sources section now render as underlined text links.

---------

Co-authored-by: Willem Jiang <willem.jiang@gmail.com>

backend/packages/harness/deerflow/agents/lead_agent/prompt.py

@@ -257,15 +257,66 @@ You: "Deploying to staging..." [proceed]
 </response_style>
 
 <citations>
-- When to Use: After web_search, include citations if applicable
-- Format: Use Markdown link format `[citation:TITLE](URL)`
-- Example: 
+**CRITICAL: Always include citations when using web search results**
+
+- **When to Use**: MANDATORY after web_search, web_fetch, or any external information source
+- **Format**: Use Markdown link format `[citation:TITLE](URL)` immediately after the claim
+- **Placement**: Inline citations should appear right after the sentence or claim they support
+- **Sources Section**: Also collect all citations in a "Sources" section at the end of reports
+
+**Example - Inline Citations:**
 ```markdown
 The key AI trends for 2026 include enhanced reasoning capabilities and multimodal integration
 [citation:AI Trends 2026](https://techcrunch.com/ai-trends).
 Recent breakthroughs in language models have also accelerated progress
 [citation:OpenAI Research](https://openai.com/research).
 ```
+
+**Example - Deep Research Report with Citations:**
+```markdown
+## Executive Summary
+
+DeerFlow is an open-source AI agent framework that gained significant traction in early 2026
+[citation:GitHub Repository](https://github.com/bytedance/deer-flow). The project focuses on
+providing a production-ready agent system with sandbox execution and memory management
+[citation:DeerFlow Documentation](https://deer-flow.dev/docs).
+
+## Key Analysis
+
+### Architecture Design
+
+The system uses LangGraph for workflow orchestration [citation:LangGraph Docs](https://langchain.com/langgraph),
+combined with a FastAPI gateway for REST API access [citation:FastAPI](https://fastapi.tiangolo.com).
+
+## Sources
+
+### Primary Sources
+- [GitHub Repository](https://github.com/bytedance/deer-flow) - Official source code and documentation
+- [DeerFlow Documentation](https://deer-flow.dev/docs) - Technical specifications
+
+### Media Coverage
+- [AI Trends 2026](https://techcrunch.com/ai-trends) - Industry analysis
+```
+
+**CRITICAL: Sources section format:**
+- Every item in the Sources section MUST be a clickable markdown link with URL
+- Use standard markdown link `[Title](URL) - Description` format (NOT `[citation:...]` format)
+- The `[citation:Title](URL)` format is ONLY for inline citations within the report body
+- ❌ WRONG: `GitHub 仓库 - 官方源代码和文档` (no URL!)
+- ❌ WRONG in Sources: `[citation:GitHub Repository](url)` (citation prefix is for inline only!)
+- ✅ RIGHT in Sources: `[GitHub Repository](https://github.com/bytedance/deer-flow) - 官方源代码和文档`
+
+**WORKFLOW for Research Tasks:**
+1. Use web_search to find sources → Extract {{title, url, snippet}} from results
+2. Write content with inline citations: `claim [citation:Title](url)`
+3. Collect all citations in a "Sources" section at the end
+4. NEVER write claims without citations when sources are available
+
+**CRITICAL RULES:**
+- ❌ DO NOT write research content without citations
+- ❌ DO NOT forget to extract URLs from search results
+- ✅ ALWAYS add `[citation:Title](URL)` after claims from external sources
+- ✅ ALWAYS include a "Sources" section listing all references
 </citations>
 
 <critical_reminders>