Harden GitHub workflows

[samdark]

Summary

• Pin GitHub Actions and reusable Yii workflow references
• Restrict workflow token permissions where applicable
• Disable checkout credential persistence where it is not needed
• Replace floating service image refs where zizmor flagged them

Validation

• zizmor --no-progress --no-exit-codes .github/workflows
• git diff --check

[Copilot]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.52%. Comparing base (68a2299) to head (88dd141).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #307   +/-   ##
=========================================
  Coverage     99.52%   99.52%           
  Complexity      313      313           
=========================================
  Files            19       19           
  Lines           838      838           
=========================================
  Hits            834      834           
  Misses            4        4           

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