fix: replace raw echo with output helpers in git/init-preview

[github-actions]

Summary

• Replaced the non-standard local die() implementation (using bare echo) with the canonical printf-based version that writes to stderr
• Added standard success() and info() output helpers
• Replaced bare echo "Using Branch: $BRANCH" with info "Using Branch: $BRANCH"
• Added success confirmation at end of successful execution chain

Closes #644

Test plan

• shellcheck git/init-preview passes
• checkbashisms git/init-preview passes
• Script behaviour is preserved — only output formatting changed

[dnyw4l3n13]

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[credfeto]

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[dnyw4l3n13]

All CI checks pass and there are no outstanding review comments. PR is ready for merge.

CI summary:

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