feat: [FEEDS-1963] regenerate from OpenAPI

[itsmeadi]

Ticket

• https://linear.app/stream/issue/FEEDS-1963

Summary

Full regen of the Java server SDK from the current chat OpenAPI spec. Adds the feeds retention policy client (get, set, delete, and run history) and the other additive model changes that have landed since the last regen: moderation rule parameters and appeals, video ring_id, poll user_id, reminder expires_at, and related fields.

Checklist

• The changed code has been covered with unit tests
• API endpoints are covered with client tests
• The internal documentation (./docs) has been updated

Notes for review

• Additive minor. ./gradlew compileJava passed on the retention client; the rest of this diff is the same generate.sh output (spotlessApply + build -x test).
• Unit tests were not run.