Add a CLI smoke test against a fixture scaffold

[theDakshJaitly]

Context

Two version bugs shipped because CI never exercises the CLI end-to-end. Add a smoke test that runs each top-level command against a fixture scaffold and asserts exit codes + basic output. This would have caught the hard-coded-version bug.

Scope

• Build a fixture scaffold (commit one, or generate via mex setup in a temp dir).
• Run each top-level command (check, doctor, timeline, log, --version, …) against it.
• Assert exit code 0 and key output substrings for each.

Where

• New test, e.g. test/cli-smoke.test.ts.
• CI already runs npm test (.github/workflows/ci.yml), so wiring is automatic once the test exists.

Acceptance criteria

• Smoke test runs all top-level commands against a fixture scaffold.
• Asserts exit codes and key output for each.
• A bad --version (e.g. mismatched constant) would fail the suite.
• npm run typecheck && npm test && npm run build pass.