Rough Idea: Add roo-cli as a Provider

Add roo-cli as a new provider/backend in ralph-orchestrator, following the same pattern as kiro and other existing backends.

This means:

• Auto-detection support (checking if roo-cli or equivalent binary is in PATH)
• CLI backend configuration (headless mode, interactive mode, prompt passing)
• A minimal preset file (presets/minimal/roo.yml)
• Integration into all the places where backends are registered (from_config, from_name, for_interactive_prompt, etc.)

The goal is to allow users to configure cli.backend: "roo" in their ralph.yml and have it work seamlessly with the roo-cli binary, similar to how kiro works with kiro-cli.