TUI Phase 2: visual iteration and available-space layout

[dyoung522]

Goal

Iterate on the prototype TUI visuals now that #31 has merged, with special attention to making individual sections/boxes use the available terminal space instead of rendering as small fixed islands.

Motivation

The Phase 1 prototype proves the command, fake data, themes, and navigation. Phase 2 should make the interface feel intentional at both 80x24 and larger terminal sizes before real service-backed data is wired in.

Acceptance criteria

• Capture/review the existing amber, wizardry, dos, and green layouts.
• Panels/sections expand to use available width where appropriate.
• Main content regions make better use of available height on larger terminals.
• Layout remains readable around 80x24.
• Default theme decision is documented, with wizardry as the likely default unless iteration shows otherwise.
• TUI layout behavior is covered by tests where practical.
• go test ./... and go vet ./... pass.

Notes

This should stay side-effect-free: continue using prototype/fake data while iterating visuals. Real service-backed integration belongs to Phase 3.

Follows docs/plans/2026-04-28-tui-implementation.md Phase 2.