fix: stop polling sleeps at the remaining deadline

[ch-z-hc]

When a pending task is near its polling deadline, poll() still sleeps for the entire configured interval. For example, a 50 ms timeout with a 1.5 s interval takes about 1.5 s to report Polling timed out. The CLI's default video polling interval is 5 s, so short timeouts can substantially overrun while waiting between requests.

Cap that sleep by the time remaining before the existing deadline. This is limited to the interval between requests: it does not change HTTP request timeouts or how completed and failed task responses are handled.

The regression fails on unchanged source (about 1504 ms) and passes with the one-line fix (about 51 ms). A separate real HTTP check against a local pending-task server took about 1543 ms on unmodified upstream and 54 ms with the patch, with one request in both cases.

Validation with Bun 1.4.0:

• Polling suite: 6 passed on Windows; typecheck and lint passed on Windows and Linux. Lint retains one existing warning in test/sdk/speech.test.ts.
• Linux production build and CI-style compiled CLI version smoke test passed.
• Full Linux suite: 597 passed, 3 failed. Unmodified a965e72 produces the same 3 failures (596 passed): two region-detection/auth tests exceed their existing 5 s test timeouts, and a FileSDK upload assertion sees a loopback base URL instead of the global endpoint. A second run with process-local loopback proxy bypass had 596 passed and 4 failed, adding an existing ImageSDK validation/network test timeout; that extra timeout is not diagnosed here. The full suite is not green. No tests were skipped or timeouts/assertions relaxed. OAuth tests used a temporary process-local no-op xdg-open to prevent launching a real browser; source and tests were otherwise unchanged.
• Two independent automated blind reviews found no actionable issues.

Codex assisted with investigation, implementation, testing and the automated reviews. These reviews are not independent human code review.