Polish ezet TUI actions and app header

[zoo3323]

What changed

• Replace the new-host and new-session keyboard shortcuts with visible, arrow-selectable action rows.
• Add direct SSH shell and new-session actions to the tmux chooser.
• Add consistent ● ezet · … app headers and update action-row colors to the existing yellow accent.
• Make empty search results escapable with the arrow keys.
• Clarify SSH password/authentication state so the spinner cannot overwrite prompts.
• Update README usage guidance and screenshots.

Validation

• make test
• Bash 3.2 syntax checks
• ShellCheck
• git diff --check
• SVG XML validation
• ezet --doctor (0 failures, 0 warnings)
• Interactive probes for the real ezet host screen and ezet 3060 tmux screen