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>

skills/public/github-deep-research/assets/report_template.md

@@ -30,6 +30,9 @@
 
 {EXECUTIVE_SUMMARY}
 
+**IMPORTANT**: Include inline citations using `[citation:Title](URL)` format after each claim. Example:
+"The project gained 10k stars in 3 months [citation:GitHub Stats](https://github.com/owner/repo)."
+
 ---
 
 ## Complete Chronological Timeline
@@ -56,6 +59,8 @@
 
 ## Key Analysis
 
+**IMPORTANT**: Support each analysis point with inline citations `[citation:Title](URL)`.
+
 ### {ANALYSIS_SECTION_1_TITLE}
 
 {ANALYSIS_SECTION_1_CONTENT}