The previous v1.83.3 changelog was generated against v1.83.0-nightly and
missed ~3 weeks of work. This regenerates it against the previous stable
release and restructures the LLM API Endpoints section to group by API
type (Responses, Batch, Count Tokens, Video Generation, Pass-Through,
etc.) matching the convention used in v1.82.3, v1.82.0, and v1.81.14.
Adds ~25 previously uncited PRs, cross-section duplications for
cross-cutting changes, and a verified first-time-contributors list.
05ad48236f