test: smoke test the packaged CLI on another platform

[afurm]

The release flow validates the package on Ubuntu CI, but Draftmora should also be easy to smoke test on another local platform such as macOS, Windows, or WSL2.

Scope:

• Add a documented smoke-test recipe or small script that installs the packed tarball in a temp directory.
• Verify draftmora starts, serves /, and responds from an API endpoint without requiring a real OpenAI key.
• Capture any platform-specific cleanup needed for the SQLite data directory.

Acceptance criteria:

• The smoke test can run without committed secrets.
• The test validates the packaged CLI path, not only npm run dev.
• Update CONTRIBUTING.md or release checklist docs with the command.