Enhancement: make TUI more btop-like (panels, sparklines, keyboard nav)

[danmaps]

The current TUI could be more like btop (modern htop) in layout, readability, and interaction.

Goals

• Dense but readable dashboard layout (panels)
• Live refresh with clear update cadence
• Keyboard-first navigation (tab/arrow/enter), consistent shortcuts
• Lightweight graphs/sparklines for key metrics
• Better color/theme defaults and accessibility (dark/light)

Possible scope

• Split screen into sections: Jobs/Queue, Recent runs/log tail, Host stats, Repo/PR status (as applicable)
• Add a help/legend overlay (e.g., ?) listing keybindings
• Add a minimal "top bar" with host + service status and last refresh timestamp

References

• btop UI patterns: panes, meters, quick toggles, help overlay

Acceptance

• A user can understand current state in <10s
• A user can navigate without mouse
• UI remains stable in small terminals (80x24)