Test the doctor command + platform/dependency probes

[ropdias]

Follow-up to #5. Builds on the vitest infra from src/core/settings.spec.ts.

Scope

src/commands/doctor.ts and the platform/dependency probes in src/infra/system.ts.

Cases to cover

doctor (src/commands/doctor.ts) — read-only diagnostics

• Reports project and global settings state: configured (tokenline block present), invalid JSON, or not configured.
• Changes nothing on disk (assert no writes / no backups in a temp dir).

system.ts probes

• checkPlatform() returns true on linux/darwin, false otherwise.
• checkBash() / checkJq() parse --version output and gate on bash ≥ 4 — mock spawnSync (or inject) so the test doesn't depend on the host having a given bash/jq version.

Notes

• These probes shell out; prefer injecting/mocking the child-process boundary over relying on the CI runner's toolchain, so the suite stays hermetic and fast.

Acceptance

• pnpm test stays green locally and in CI.
• The cases above are covered.