Responsive layouts for phone and tablet

[RaistlinMuc]

Summary

• Add responsive phone layout with a bottom tab bar for Projects/Codex/Git/Log.
• Add a tablet layout with a nav rail, resizable Projects column, and full-height main view.
• Introduce layout mode hook, new styles, and icons; lower the minimum window size to support small screens.

Motivation

Make CodexMonitor usable on small and medium window sizes without losing core navigation and workspace context.

Testing

• Not run (local environment).