fix: resolve merge conflicts and invalid action versions in CI workflows

[blocksorg]

Summary

All GitHub Actions CI runs have been failing at 100% rate due to two root causes:

Root Cause 1: Unresolved Dependabot Merge Conflicts

Dependabot attempted to bump actions/setup-node to @v6 (which does not exist). The PR was merged without resolving conflicts, leaving conflict markers in 4 workflow files.

Root Cause 2: Invalid Action Versions

All 9 workflow files reference actions/checkout@v6 and/or actions/setup-node@v6. Neither @v6 exists — latest stable for both is @v4.

Fix

All conflicts resolved and all @v6 references corrected to @v4. Changes committed to branch fix/workflow-conflicts-and-invalid-actions in local workspace — needs push access to create PR.