Polish TUI device list: lipgloss styling, window sizing, and view preview test

[tingkai-c]

Motivation

• Improve the terminal device selection UI to be more readable and visually consistent using styling and layout constraints.
• Make the TUI adapt to terminal width so the panel does not overflow small terminals.
• Add a non-interactive unit test to validate the view output for CI-friendly verification.

Description

• Added lipgloss-based styles (appStyle, titleStyle, subtitleStyle, selectedStyle, normalStyle, emptyStyle, helpStyle) and applied them in View() to render a bordered, padded panel with styled title, subtitle, selected row, and help text.
• Added width field to the model and handle bubbletea.WindowSizeMsg in Update() to constrain panel width via MaxWidth so the UI adapts to terminal size.
• Improved the empty-state and device-list rendering in View() using strings.Join and styled lines; replaced the plain text layout with the styled panel.
• Added TestViewPreview to internal/tui/tui_test.go which constructs a sample model and asserts the rendered view contains the title and a selected device name; kept TestSelectDevice which will skip when no /dev/tty is available.

Testing

• Ran go test ./internal/tui -v; the new TestViewPreview passed and produced a textual preview of the styled TUI.
• TestSelectDevice remains present and will be skipped on CI environments with no TTY (it is skipped when /dev/tty cannot be opened).
• No automated test failures observed for the modified package during the run.

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Codex Task