feat(tui): Bash checkbox menu (#495 Slice 2)

[primetimetank21]

Summary

Implements Slice 2 of #495: the Bash interactive checkbox menu for Linux/macOS/WSL.

Depends on merged #504 (Slice 1) — all non-interactive guards, TTY detection, and the --selection-file seam landed in Slice 1.

Part of #495

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What ships in this PR

scripts/linux/lib/tui.sh (new)

Sourced by setup.sh. Two navigation modes:

• Bash >=4.2: arrow up/down, Space to toggle, Enter to confirm, q/ESC to cancel. ANSI cursor repositioning redraws the list in place.
• Bash 3.2 fallback: numbered-toggle line mode. _TUI_ARROW_NAV_OVERRIDE=0 env var forces this path for testing without needing a real bash 3.2 environment.

Default tools are pre-checked and labeled (default); opt-in tools (available but not default) are unchecked and labeled (opt-in), sorted alphabetically.

Cancel exits 0 with Install cancelled.
Empty confirm exits 0 with Nothing selected, exiting.
Selection feeds the existing build_final_toolset engine via ARG_ONLY; order is always preserved by DEFAULT_TOOLS sequence.

scripts/linux/setup.sh (modified)

• Sources lib/tui.sh alongside lib/log.sh.
• main() now calls show_tool_menu when interactive, or reads from --selection-file (CI seam) without rendering the menu.
• Updated stale Slice 1 comment.

tests/test_tui_bash.sh (new)

13 tests covering:

Test	Type	Covers
T_tui_sh_sources_clean	smoke	tui.sh sources without error
T_menu_resolve_defaults	integration	all defaults selected → run-log == defaults.txt
T_menu_resolve_subset	integration	reversed-input subset → order preserved
T_menu_resolve_optin	integration	opt-in tool appended after defaults
T_menu_resolve_empty	integration	empty selection → exit 0, "Nothing selected"
T_menu_selection_file_e2e	integration	selection-file seam → correct ordered run-log
T_menu_cancel_aborts	unit	_MENU_CANCELLED=1 guard → exit 0
T_menu_noop_empty	unit	empty _MENU_SELECTION guard → exit 0, correct message
T_numbered_render_runs	unit	_tui_numbered_render draws list with states and labels
T_render_list_runs	unit	_tui_render_list renders cursor, checkboxes, labels
T_noninteractive_compat	regression	--non-interactive still runs defaults (Slice 1 compat)
T_selection_file_no_noninteractive_conflict	regression	--non-interactive + --selection-file → error
T_help_no_selection_file	regression	--help does not expose hidden --selection-file

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Excluded from this PR

• Slice 3: PowerShell 5.1 ASCII menu (lib/tui.ps1, Resolve-FinalToolset). Separate branch.
• Slice 4: docs additions (README, ARCHITECTURE). No changes to those files in this PR.
• No changes to PowerShell scripts, docs, or CI workflow files.

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CI validation

ShellCheck passes locally via pre-commit hook and pre-push hook (both ran successfully on commit and push).

CI will run on Ubuntu (bash 5.x) and macOS (bash 3.2):

• lint-shell-scripts job: shellcheck on setup.sh + tools; test_setup_flags.sh
• validate-linux / validate-macos: existing install and flag tests

test_tui_bash.sh is wired into validate-linux (Ubuntu, bash 5.x) and validate-macos (macOS, bash 3.2) via a Run TUI bash menu tests step in .github/workflows/validate.yml. All 13 tests gate both jobs on every push and pull request.

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Manual verification required (not covered by automated tests)

The following cases require a live interactive TTY and are not verified by CI or this PR's automated tests:

1. Arrow-key navigation on bash 5.x (Ubuntu/Linux terminal) — up/down moves cursor, Space toggles, Enter confirms.
2. ANSI in-place redraw in tmux / screen.
3. Numbered-toggle mode on macOS bash 3.2 (Terminal.app) — enter a number, a, Enter, q.
4. ESC / Q cancel from within the rendered menu.
5. "All defaults checked + Enter" produces identical install to a no-arg run.
6. Opt-in tool checked produces correct install appended after defaults.

These cases are documented here rather than claimed as tested.