Prime sudo before running the Homebrew installer

[mhfs]

The failure

Bootstrapping a freshly reformatted macOS 27 laptop aborted immediately:

==> Detected macOS 27.0 (arm64)
==> Installing Homebrew (this also installs the Xcode Command Line Tools)
==> sudo will ask for your password
==> Running in non-interactive mode because `$NONINTERACTIVE` is set.
==> Checking for `sudo` access (which may request your password)...
Need sudo access on macOS (e.g. the user mhfs needs to be an Administrator)!
error: Homebrew installation failed

Why

The account is an administrator — Homebrew's message is a red herring. We
invoke the installer with NONINTERACTIVE=1, and its have_sudo_access()
reacts to that by adding -n to sudo:

elif [[ -n "${NONINTERACTIVE-}" ]]
then
  SUDO+=("-n")
...
  "${SUDO[@]}" -l mkdir &>/dev/null

sudo -n fails outright instead of prompting. A machine that has just booted
has no cached sudo timestamp, so the pre-flight check fails and the installer
aborts. The ==> sudo will ask for your password line we printed one line
earlier was wrong for the same reason: NONINTERACTIVE=1 is precisely what
stopped it from asking.

This reproduces on any freshly booted Mac, so it hits every first-run
bootstrap — the exact case this script exists for.

The fix

Prime the sudo timestamp ourselves with a prompt-capable sudo -v before
handing off. Only the pre-flight check needed it: the installer's privileged
commands go through execute_sudo, which calls /usr/bin/sudo without
-n, so they re-prompt on their own if the timestamp expires during the
Command Line Tools download later in the run.

Details worth a look while reviewing:

• prime_sudo opens with sudo -n -v, so a warm timestamp (or a passwordless
  sudo rule) short-circuits and we never announce a prompt that will not come.
• The failure path is if sudo -v; then rather than sudo -v || die, because
  under set -euo pipefail the latter exits on sudo's status before the die
  diagnosis is ever printed.
• On failure we now point at the one thing that would genuinely cause it —
  the account not being an administrator.

Testing

Not yet verified end to end on a clean macOS install — that is what keeps this
a draft. bash -n passes; the reasoning above is from Homebrew's current
install.sh. Worth a run on a fresh machine, or at least sudo -k followed by
the bootstrap command, before this merges.

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