fix: replace raw echo with standard output helpers in git/switchtomain

[github-actions]

Summary

• Added die, success, and info helper functions to git/switchtomain
• Replaced all raw echo calls with the appropriate output helper
• Fixed [ ! -z ... ] → [ -n ... ] for shellcheck/checkbashisms compliance
• Behaviour is preserved: the "no default branch" case still continues to the next repository (uses info not die)

Closes #649

Test plan

• shellcheck git/switchtomain passes
• checkbashisms git/switchtomain passes
• Script output now uses coloured → / ✓ / ✗ indicators instead of plain echo

[dnyw4l3n13]

All CI checks passed. PR is now ready for review.

Summary of changes:

• Added die, success, and info output helper functions to git/switchtomain
• Replaced all raw echo calls with the appropriate helpers
• Fixed [ ! -z ... ] → [ -n ... ] for shellcheck/checkbashisms compliance
• Behaviour preserved: "no default branch" case uses info (not die) so the loop continues to the next repository

[credfeto]

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