ci: update actions to Node 24 runtimes

[OgeonX-Ai]

Summary

• update actions/checkout from v4 to immutable v5 SHA
• update actions/setup-python from v5 to immutable v6 SHA
• preserve explicit least-privilege permissions (contents: read)

Validation

• 30/30 unit tests passed
• 9/9 reference-product tests passed
• golden corpus 8/8 passed
• adversarial corpus 6/6 passed
• deterministic release verification passed
• both pinned action manifests declare Node 24 runtimes
• git diff --check passed