refactor: move node-canvas integration to standalone repo

[clfhhc]

Summary

• remove the non-React node-canvas integration package from this repository
• narrow aggregate build/test/release scripts to the sole @graphrefly/react root package
• transfer canonical source and release ownership to graphrefly/graphrefly-reactive-layout-node-canvas under D662

Proof

• pnpm lint
• pnpm typecheck
• pnpm test:all (59 tests)
• pnpm build:all (ESM/CJS/DTS package smoke)
• pnpm dashboard:check
• repository-wide ownership search has no remaining node-canvas package/checker references

The standalone repository main CI is green before this cutover: https://github.com/graphrefly/graphrefly-reactive-layout-node-canvas/actions/runs/30409332934