[feat]: Add CodeRabbit AI code review integration

[yashdev9274]

Feature Summary

Add CodeRabbit AI code review integration to Emdash, enabling AI-powered code reviews directly within the application, similar to how Cursor integrates CodeRabbit for inline code reviews.

Problem or Use Case

Currently, Emdash orchestrates multiple coding agents but lacks built-in AI code review capabilities. Users need to:

• Manually run CodeRabbit CLI outside of Emdash
• Or rely solely on GitHub App PR reviews (which only work after code is pushed)

It would be helpful if Emdash could trigger CodeRabbit reviews locally within worktrees before commits/PRs, displaying results directly in the UI.

Proposed Solution

Implement CLI-based CodeRabbit integration that allows running local code reviews on worktrees:

Phase 1: Service & IPC

• Create CodeRabbitService.ts to wrap the cr CLI
• Handle CLI detection, authentication, and review execution
• Create IPC handlers for: coderabbit:checkInstalled, coderabbit:runReview, coderabbit:auth

Phase 2: UI Integration

• Add "Review with CodeRabbit" button to Changes panel and Command Palette
• Create review panel to display findings categorized by: Security, Performance, Best Practices, etc.
• Click comments to navigate to file/line

Phase 3: Configuration

• Auto-generate .coderabbit.yaml for new worktrees
• Allow customization via project settings

UI/UX Design

• Trigger: Button in Changes toolbar + Command Palette (Cmd+Shift+R)
• Display: Side panel with categorized issues, click to navigate

See coderabbit-plan.md for detailed implementation plan.

Alternatives Considered

1. GitHub App only - Already works but only reviews after PR creation, not local changes
2. Add as provider - Could add CodeRabbit as agent in registry, but CLI review is simpler
3. External script - Users could run CodeRabbit externally, but loses UI integration

Additional Context

• CodeRabbit CLI documentation: https://docs.coderabbit.ai/cli/reference
• CLI can review: all, committed, or uncommitted changes
• Output formats: interactive, plain text, or minimal (for AI agents)
• Config: .coderabbit.yaml in project root