fix: fail builds after generation errors

[OskarEichler]

Summary

• set a nonzero process exit code when the build pipeline catches a generation error
• add a regression test covering a rejected Rollup build

Problem

The build entrypoint catches generation failures and logs them, but then exits successfully. CI or release automation can therefore treat an incomplete build as valid.

Breaking changes

Build commands that encounter a generation error now exit unsuccessfully instead of returning status 0. Runtime APIs and generated package behavior are unchanged.

Verification

• regression test fails on current dev and passes with this change
• npm test: 94 suites, 795 tests passed
• npm run lint
• NODE_OPTIONS=--openssl-legacy-provider npm run build
• git diff --check