fix: treat omitted autoResolutionMs as no auto-resolution

[2409324124]

Summary

Fixes #344.

• request_user_input was aborted immediately with {answers:{}} when autoResolutionMs is omitted, before the client could render the form.
• Root cause in requestUserInputElicitation: the blocking path was gated on params.autoResolutionMs === null. When Codex omits the field it arrives as undefined, so the code fell through to the timeout path where undefined ?? 0 schedules an immediate resolveWithoutInput; the abort wins Promise.race on the next tick.
• Change: treat both null and undefined as "no auto-resolution" via == null. Explicit numeric autoResolutionMs timeout behavior is unchanged.

Tests

• Added a regression test in src/__tests__/CodexACPAgent/elicitation-events.test.ts: with autoResolutionMs omitted and a client answer arriving after 200ms, the handler must wait for the client instead of aborting. On the current code it returns {answers:{}} in ~11ms; with the fix it waits ~200ms and returns the client's answers.
• npm test (435 passed, 28 skipped)
• npm run typecheck

Note on e2e coverage

This is not covered by an e2e test. request_user_input is emitted by a real Codex session during interactive flows, so deterministically reproducing the omitted-field case requires injecting the protocol message rather than driving a live model (which would also need OPENAI_API_KEY). The mock-fixture unit test above does exactly that, matching the runtime shape Codex actually sends.