Fix workflow timestamp check to use frontmatter hash when .md is newer

[Copilot]

The workflow timestamp checker failed immediately when the .md file was newer than the lock file, ignoring the frontmatter hash. This caused false positives when only documentation or non-frontmatter content changed.

Changes

Updated check_workflow_timestamp_api.cjs logic:

• When md timestamp > lock timestamp: Check frontmatter hash first
  • Hash match → up to date (only non-frontmatter changed)
  • Hash mismatch → outdated (recompilation needed)
  • Hash unavailable → fail conservatively
• Other cases unchanged (same commit SHA, equal timestamps, lock newer)

Updated error messages:

- Lock file is outdated! Frontmatter hash mismatch detected.
+ Lock file is outdated! The workflow file '.github/workflows/X.md' frontmatter has changed.

Test updates:

• Added tests for hash matching when md is newer
• Updated assertions for new error message format
• Added test for hash check failure handling

Original prompt

Review the JavaScript script that checks if agentic workflow files are outdated. Make sure the following holds:

• first check time stamp on commits between lock file and .md file. If the lock file is same or older, it is up to date.

• if the .md file is older, do a frontmatter hash check.

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