feat(setup): add TUI picker non-interactive guard

[primetimetank21]

Summary

• add Bash and PowerShell interactive/non-interactive flags and headless guards
• add hidden selection-file seam while keeping hidden seams out of help
• forward new flags through root entry points
• add ordered-selection drift gates to CI for Bash and PowerShell 5.1

Part of #495.

Corrective revision

• Rewrote 4 Bash skip-path unit tests to capture exact exit status 1 instead of ! is_interactive; added \T_menu_skip_guards_127\ mutation guard proving exit-127 is distinct from exit-1
• Added --interactive + --selection-file\ bypass in \is_interactive\ (Bash) and \Test-ShouldShowMenu\ (PowerShell) so CI can exercise the menu path without a TTY; precedence chain preserved (non-interactive/only/skip still suppress first)
• Added \T_menu_selection_file_ci_bypass\ (Bash) and \T_menu_selection_file_ci_bypass_ps\ (PS) proving bypass under headless/CI conditions
• Removed duplicate PS selection-file resolution block; file is validated, names joined, then routed through the existing canonical -Only\ path

Deliberate exclusions

• no checkbox menu, key handling, rendering, or console reads
• no \Resolve-FinalToolset\ extraction yet
• interactive mode without a selection file still runs current defaults

Validation

• \�ash tests/test_setup_flags.sh\ - 50 passed (+2)
• \powershell -File tests\test_setup_flags_pwsh.ps1\ - 50 passed (+1)
• ShellCheck - passed
• PSScriptAnalyzer for production setup scripts - passed (advisory warnings in test file are pre-existing)
• PowerShell 5.1 parse and ASCII checks - passed

Compatibility and drift notes

• default tool order remains fixture-gated; selection-file input is filtered through the existing ordered engine
• repository .gitattributes\ currently enforces CRLF for .ps1; this PR keeps that current policy. Bash files remain LF; PowerShell files remain ASCII-only with final newlines.

Gates for later slices

• keep all Bash and PowerShell flag compatibility suites green
• use the hidden selection-file seam for menu integration tests
• do not expose hidden seams in help
• preserve no-flag CI/headless behavior and ordered dispatch