ci: publish package to GitHub Packages

[BenKalsky]

Summary

• Adds a manual GitHub Packages publish workflow
• Repackages npm tarball as @digitizers/sumit-react for npm.pkg.github.com
• Uses GITHUB_TOKEN with packages: write so the package appears in the repo sidebar

Test Plan

• corepack pnpm test
• corepack pnpm typecheck
• corepack pnpm build
• npm pack --dry-run

[chatgpt-codex-connector]

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Reviewed commit: 855090b35a

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[chatgpt-codex-connector]

Keep install registry on npmjs before build steps

Setting registry-url to https://npm.pkg.github.com at setup time makes all subsequent pnpm install steps resolve packages from GitHub Packages instead of npmjs, so standard dependencies like react are looked up at npm.pkg.github.com and fail (403/404). In this workflow, installs happen immediately after setup (Build sumit-api peer package and Install sumit-react), so the publish job will fail before packaging unless the registry is switched back or scoped only to the publish step.

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