feat(npm/runtime): revert back to CJS

[Boshen]

This package was originally designed for dual export with cjs entry. Keep it this way.

[graphite-app]

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[Copilot]

Pull Request Overview

Revert npm/runtime package to CommonJS default while keeping dual-export support.

• Switch package.json "type" from "module" to "commonjs"
• Aim to maintain dual export (CJS entry) behavior via exports map

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[Copilot]

Changing the package type from module to commonjs alters how Node treats .js files and can break ESM consumers that relied on the package being ESM by default; this should be treated as a breaking change. Please bump the package with a semver-major release and note the change in the changelog.

[Copilot]

[nitpick] Update the package README/CHANGELOG to document that the package defaults to CommonJS and provide clear import/require examples for both ESM and CJS consumers. This helps users adapt to the change and reduces integration friction.