TUI responsiveness: smooth degradation across terminal sizes

[Antoinegtir]

Why

Resize works, but the TUI still feels rigid at the edges:

• At narrow widths some keybinds in the footer disappear even though there is room left.
• The header truncates abruptly instead of degrading gracefully.
• Device panel does not reflow when the right-side panel (perf / network) is hidden.
• Long device names overflow the left column on tiny terminals.

What we want

• Smooth degradation: every panel knows its own minimum width and collapses cleanly.
• Footer packing should never leave horizontal whitespace bigger than a separator.
• Header should show as much identity as fits; never blank out.
• Re-test in 80x24, 120x30, 200x50, and ultra-wide (300+).

Acceptance

• Manual matrix passes on the four sizes above.
• No dashboard stacking on rapid resize.
• Snapshot tests (if/when we add them) cover three widths.