Harden GitHub workflows

[samdark]

Summary

• Pin reusable Yii workflow and action references
• Restrict workflow token permissions to read-only contents where applicable
• Disable checkout credential persistence where it is not needed

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 100.00%. Comparing base (8f2ecd0) to head (bd0f786).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##              master       #20   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
  Complexity       100       100           
===========================================
  Files             23        23           
  Lines            253       253           
===========================================
  Hits             253       253           

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