feat: set PR review reasoning effort to high - #4

After an initial 502/503/504%2C the strict retry without reasoning only falls back to legacy JSON when that retry also returns a gateway status. If the retry instead returns 400 or 422 because the endpoint rejects Structured Outputs%2C the code re-raises and fails%2C even though those statuses trigger compatibility fallback on the initial request and the documentation promises a legacy fallback after the gateway retry. Suggestion%3A Handle `CAPABILITY_FALLBACK_STATUS_CODES` from the strict no-reasoning retry as a reason to issue the legacy `json_object` request as well. Add a regression test for the sequence 502/503/504 followed by 400/422 followed by a successful legacy response.