feat(plugins): implement Sprint 5 documentation and fixes (#266-#269)

Documentation:
- Add git-flow branching strategy guide (docs/BRANCHING-STRATEGY.md)
- Add clarity-assist ND support documentation (docs/ND-SUPPORT.md)
- Update DEBUGGING-CHECKLIST.md with Gitea auto-close behavior and MCP restart notes
- Update plugin READMEs to reference new documentation

Bug Fix:
- Add milestone parameter to update_issue MCP tool (gitea_client.py, server.py, tools/issues.py)

Closes #266, Closes #267, Closes #268, Closes #269

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

plugins/git-flow/README.md

@@ -119,6 +119,10 @@ The git-assistant agent helps resolve merge conflicts with analysis and recommen
 → Status: Clean, up-to-date
 ```
 
+## Documentation
+
+- [Branching Strategy Guide](docs/BRANCHING-STRATEGY.md) - Detailed documentation of the `development -> staging -> main` promotion flow
+
 ## Integration
 
 For CLAUDE.md integration instructions, see `claude-md-integration.md`.