[FIX] Skip Homebrew bootstrap confirmation prompts

[hmvege]

Full macOS setup previously invoked Homebrew's installer without its unattended setting, causing a RETURN/ENTER confirmation prompt when Homebrew was missing.

Set NONINTERACTIVE=1 to skip normal confirmation and password prompts. Preserve stdin so Homebrew's interactive Command Line Tools fallback remains available when run from a terminal if automatic installation fails. Actual installer failures still stop setup through the existing set -euo pipefail, with output and errors visible.

Applies to full CLI and full GUI bootstrap. Existing Homebrew and lite behavior are unchanged. No README changes.

Validation:

• bash tests/smoke-unix.sh passed for all platform templates and setup modes, plus existing behavior checks.
• A temporary bootstrap check with a pseudo-terminal confirmed that the installer receives NONINTERACTIVE=1 and retains terminal stdin.
• git diff --check passed.
• Fresh macOS installation and the actual GUI fallback were unavailable in this Linux environment.

Reference: https://docs.brew.sh/Installation#unattended-installation