Update CI actions and remove obsolete status notes

[mackysoft]

Summary

• Replace deprecated Node.js 20 action runtimes in CI and release workflows with current Node.js 24 versions.
• Remove the obsolete January project status document.

Scope

• Update checkout to v7, cache to v6, upload-artifact to v7, download-artifact to v8, and create-github-app-token to v3.
• Use the App token action's client-id input. Its implementation passes this value to Octokit's appId option, and GitHub accepts the existing App ID as the JWT issuer. Token permissions remain scoped to repository contents.
• Pin Release's preparation and publication jobs to Ubuntu 24.04. Unity jobs retain Ubuntu 22.04 and their existing Editor versions, commands, cache keys, and artifact paths.
• Delete STATUS.md.

Verification

• Checked all 13 updated action steps against the current official action.yml files: each uses Node.js 24, supplies its required inputs, and has no unknown inputs.
• Checked workflow syntax and expressions with actionlint 1.7.12. Its embedded App-token schema produces four outdated app-id/client-id findings; the current v3 metadata explicitly makes app-id optional and accepts client-id. No other findings and no repository lint suppression added.
• git diff --check passed.
• Hosted validation passed for 99911e0: Unity 2021.3.45f2 passed 198/198; Unity 6000.6.6f1 passed 208 with two pre-existing Explicit variance reproductions skipped. Verification passed. Every completed job has zero annotations, and neither Editor log contains a native crash.
• Assets, Packages, and ProjectSettings are identical to the built 2.0.0 release commit. The previous workflow timed out twice on its 2021.3 run, with native crash reporting in the first Editor log; its exact stop cause remains unestablished. The updated workflow passes with the same Unity inputs, without changing assertions, timeouts, or retry behavior.
• The updated Release actions have been checked against their upstream contracts; Release has not been dispatched from this maintenance commit.

References

• GitHub Actions Node.js 20 deprecation
• Current App-token action inputs
• GitHub App JWT issuer requirements