ci: publish mtmcanvas through npm release workflow

[codeh007]

Summary

• Add a dedicated mtmcanvas-v<version> npm release workflow.
• Reuse the repository's NPM_TOKEN, npm provenance publication, and registry integrity/version read-back gates.
• Make root pnpm check validate both mtmharness and mtmcanvas.

Related issue: codeh007/gomtm#664

Verification

• actionlint .github/workflows/release-mtmcanvas.yml passed.
• Individual mtmharness and mtmcanvas checks passed before this workflow-only change.
• The workflow is restricted to annotated mtmcanvas-v<version> tags and verifies the tagged commit is an ancestor of origin/main before publishing.

[coderabbitai]

Important

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Plan: Pro Plus

Run ID: c19b4d7e-93a7-4a42-a5ab-37139932c92e

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