feat: accept validated artifacts in the release workflow

[exKAZUu]

Requirements

• required: Improve reusable-workflows where necessary to release commitkv to npm through wbfy and semantic-release.
• required: Complete PRs through review-booster, complete-pr, and release, in that order.
• chosen: Accept an optional artifact from the caller's current workflow run so cross-platform packages can be tested before the standard release job publishes them.
• chosen: Treat an empty artifact_path as omitted, because GitHub inputs can override defaults with an empty string and download-artifact would otherwise extract into the repository root.
• required: Existing callers without an artifact must keep their current release behavior.

Self Check

• I've confirmed All checks have passed on this page.
• I've reviewed my changes on the GitHub diff view.
• I've written the steps to test my changes.
• I've added screenshots (if the UI changed).

Steps to Test

1. Run bun run verify-full and bun run test (both passed locally); the PR's actionlint check passed.
2. Call the release workflow after uploading an artifact, with artifact_name and optionally artifact_path. Confirm it is downloaded before the build and release scripts. The commitkv release pipeline exercises this handoff end to end.
3. Confirm callers omitting artifact_name skip the download. An omitted or empty destination uses .tmp/release-artifacts; the pinned action source was inspected to confirm why forwarding an empty path would otherwise select the repository root.

[gemini-code-assist]

Note

Gemini is unable to generate a review for this pull request due to the file types involved not being currently supported.