AX-2134: replace release-please with version-file diff

[YoniMelki]

Summary

• Replace release-please + Conventional Commits with a version-file trigger (package.json vs latest strict vX.Y.Z tag).
• Remove release-please-config.json, .release-please-manifest.json, and pr-title.yml.
• Bump 0.3.0 → 0.3.1 so merge is the first end-to-end run (GitHub Release + publish-as-is.yml OIDC publish).
• PR-time X.Y.Z check; publish dispatch now passes the commit SHA and publish-as-is.yml checks that ref out (plus concurrency).
• CONTRIBUTING no longer claims Conventional Commits are CI-enforced; CHANGELOG frozen as of v0.3.0; mise version task defaults to a plain patch bump.

Part of AX-2134.

Landing

Merging cuts v0.3.1 and should publish that version to npm. After that, every merge must bump package.json or Release fails.

Repo settings: if ValidatePrTitle is still a required status check, remove it — that workflow is gone.

Test plan

• Confirm merge creates GitHub Release v0.3.1 and dispatches publish-package-as-is.
• Confirm npm publishes 0.3.1 via OIDC (publish-as-is.yml filename unchanged).
• Confirm PR-time check rejects a non-X.Y.Z version.
• Confirm branch protection does not wait on ValidatePrTitle.