fix(create): quiet scaffold output behind the spinner

[DylanPiercey]

Follow-up polish to #235. The scaffold was leaking raw pnpm/git internals through the clack UI:

[ERR_PNPM_IGNORED_BUILDS] Ignored build scripts: esbuild@…
… Running postinstall script, done
Already up to date
. prepare$ husky
│ .git can't be found
git version 2.50.1
fatal: not a git repository (or any of the parent directories): .git

Now the install and git steps run captured behind the spinner, which just transitions Downloading → Installing dependencies with pnpm → Setting up git repository → Project created. Install output is surfaced only if it genuinely fails.

exec gained a capture mode; git commands and both install passes use it. Verified end-to-end: clean output, esbuild still approved/built, git still initialized, app still builds.

[changeset-bot]

🦋 Changeset detected

Latest commit: b966785

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@marko/create	Patch
create-marko	Patch

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