chore: build before publish (prepack guard + green build)

[heskew]

Makes npm run build exit clean so it can guard publishes — 0.5.0 shipped without dist/ because nothing built before npm publish.

• prepack: "npm run build" — npm publish/npm pack now always build dist/ first; a buildless publish can't happen again.
• Cleared the pre-existing build errors so the guard doesn't block publish: skipLibCheck (3 @types/node lib-internal errors), targz.ts Buffer→Uint8Array, and run.ts reporter compose(new spec()) — it was passing the reporter class (this also fixes the spec output, which I confirmed renders correctly).
• CI now gates check + build alongside the tests across the matrix.

Verified locally: check/build exit 0, 15/15 tests pass, and npm pack rebuilds dist/ via prepack after rm -rf dist.

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🤖 Generated with Claude Code

[gemini-code-assist]

Code Review

This pull request adds a prepack script to package.json, instantiates spec in src/run.ts, updates the chunk types to Uint8Array in src/targz.ts, and enables skipLibCheck in tsconfig.json. The review feedback highlights a potential issue in src/targz.ts where stream errors are not handled, which could cause the Promise to hang indefinitely. It is recommended to handle errors on both the pack and gzip streams.

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