`cloud connect` AWS CloudFormation background wait returns 'pending' without a non-zero exit code

[justinhelmer]

Follow-up from the review of #77 (fix for #75).

src/commands/cloud/connect.ts can end the AWS CloudFormation leg with outcome 'pending' (stack still creating when the background wait gives up) without setting process.exitCode, so the process exits 0 although no account is connected yet. Same soft-failure-exits-0 class as #75: scripts and the installer's funnel read it as success.

Decide whether pending should exit non-zero (it is not a completed connect) or at least a distinct documented code, add the settledExitCode() path from #77 to it, and cover it with the same subprocess test shape (test/exit-code.test.ts).