- Add base_branch detection to WorktreeInfo (from project root HEAD)
- Expose base_branch in AgentInfo API response
- Add {{base_branch}} template variable to agent config rendering
- Show git difftool command with copy-to-clipboard in AgentPanel UI
- Add diff command instruction to coder agent prompts
- Add AgentPanel tests for diff command rendering and clipboard
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
