perf: What's New browse payload is ~680 KB raw (172 KB gzipped); page or trim server-side #1869

What: With the cleaned generator, the real GET /api/v1/changelog/all response is about 682 KB raw / 172 KB gzipped for 171 versions (the spec estimated ~40 KB). The browse dialog pages 10 versions at a time, but only client-side, so the full payload is fetched on open.

Where: backend/internal/changelog/changelog.go (GetAllEntries), backend/internal/api/handlers/changelog_handler.go (All), frontend/src/hooks/useChangelog.ts.

Severity: low

Suggested approach: Server-side paging (?limit=&cursor=) for /changelog/all, and/or trim the other bucket from the browse payload. Found while reviewing the What's New pipeline PR (docs/plans/current_spec.md).