ci: adopt central Node.js 24 Actions

[jinon86]

Summary

• replace mutable GitHub Action tags with official Node.js 24 Action commits pinned to full immutable SHAs from jinwon-int/github-workflows/action-lock.json
• add weekly Dependabot updates for the github-actions ecosystem
• preserve existing triggers, matrices, commands, permissions, and application behavior

Public/private boundary

This repository is public while jinwon-int/github-workflows is private. GitHub does not resolve private cross-repository actions from public workflows, so this PR intentionally uses the approved official full SHAs directly instead of private central composite wrappers.

Validation

• central schema-aware Action audit: violations 0
• remaining mutable remote Action refs: 0
• actionlint: no findings
• git diff --check: clean
• previous failed run was isolated to Unable to resolve action jinwon-int/github-workflows, not found before any project command executed

Safety

• workflow/configuration source only
• no release, deployment, provider send, secret, permission, or data mutation
• Dependabot keeps the immutable public pins current through reviewed PRs

Related to jinwon-int/github-workflows#1.

[seoseo-ai]

Reviewed final immutable Node.js 24 Action migration head. Repository CI is fully green, central schema-aware audit reports zero violations, mutable refs are zero, and check-run annotations/deprecations are zero.

[jinon86]

Closing unmerged because the active ruleset requires one approval from a reviewer with write access, while seoseo-ai currently has read access. No admin bypass or permission change will be used. The identical final commit ae58a75 is being resubmitted from the seoseo-ai fork so jinon86 can provide a qualifying independent review.