TUI presentation: terminal colors and visual polish for interactive picker

[primetimetank21]

Summary

Add tasteful, accessible terminal colors and visual polish to the TUI tool picker (bash and PowerShell) to improve visual presentation and readability once the functional implementation lands.

This is deferred work and must not expand or be merged into PR #505 (Slice 2) or PR #506 (Slice 3). This issue captures color/styling enhancements as a follow-up after functional TUI work is complete.

Why

The interactive picker will be functional but visually minimal. Terminal colors, contrast improvements, and subtle visual polish can enhance the user experience and readability without compromising cross-platform compatibility.

Scope

• Add tasteful, accessible terminal colors to highlight selections, confirm actions, and distinguish disabled options.
• Preserve ASCII-only compatibility (no Unicode box-drawing required, though allowed if PS 5.1-safe).
• Preserve PowerShell 5.1 compatibility (no Out-GridView or modern console ANSI dependencies required).
• Maintain no-color / non-TTY behavior (graceful fallback when colors are disabled or unavailable).
• Ensure readable contrast ratios for accessibility.
• No added runtime dependencies unless justified (e.g., colorize library only if color output cannot be implemented natively).

Out of scope

• Expanding or modifying the functional implementation of PR feat(tui): Bash checkbox menu (#495 Slice 2) #505 or PR feat(windows): PS 5.1 ASCII picker, Resolve-FinalToolset, TUI tests [Slice 3] (#495) #506.
• Re-opening styling discussions for closed TUI work.
• Adding Unicode / box-drawing that breaks PS 5.1 or non-Unicode terminals.

Blocked by

• Completion of TUI tool picker: interactive keyboard-driven install menu (Phase 2 of #468) #495 Phase 2 (PR feat(tui): Bash checkbox menu (#495 Slice 2) #505 — Bash picker) and Phase 3 (PR feat(windows): PS 5.1 ASCII picker, Resolve-FinalToolset, TUI tests [Slice 3] (#495) #506 — PowerShell picker).

---

Due date / sprint: To be triaged.