feat: Ralph Loop support for OpenCode and other external CLIs

[sonikro]

Summary

The Ralph Loop autonomous task execution feature currently only works with Claude Code. Users who prefer OpenCode, Codex, Gemini, or other AI CLI backends cannot use this autonomous workflow capability.

The Need

Developers using OpenCode or other external CLI harnesses should be able to start Ralph Loops with full todo tracking, completion detection, iteration management, and circuit breaker support — just like Claude Code users can today.

Acceptance Criteria

• Users can start a Ralph Loop using OpenCode as the backend
• Users can start a Ralph Loop using other supported external CLIs (Codex, Gemini, etc.)
• Todo tracking, completion detection, and iteration management work across all supported backends
• The experience is consistent regardless of which AI CLI backend is selected