test(e2e): add library mode smoke tests

17 e2e tests that verify the bundled output works as a library:
- Bundle structure (no shebang, no warning suppression in library)
- Export shape (sentry, createSentrySDK, SentryError, SentryOptions)
- Variadic API (version, env isolation, error wrapping)
- Typed SDK (namespace methods, auth error handling)
- Type declarations (.d.cts content)

All tests run the bundled dist/index.cjs via Node.js subprocesses
to verify real npm package behavior.

Author: BYK