orbit documentation

• Features: everything orbit does, in detail.
• Usage: commands, and editing orbit.yaml while orbit runs.
• Keys: keyboard shortcuts of the TUI.
• Configuration: orbit.yaml reference, editor support, hooks, environment variables, healthchecks.
• Git: the Git view and multi-repo actions.
• Plugins: install and use plugins, and write one.
• Themes: built-in themes and writing your own.
• Scripting & editors: the local socket and its JSON-RPC protocol.
• AI agents: the optional skill so coding agents can drive orbit.
• Platforms: differences between Linux, macOS and Windows.
• Upgrading from 0.x: moving from the TypeScript version.

To contribute, see CONTRIBUTING.md.