* fix(github): prevent PR cache sync from exhausting all pages
* refactor(github): derive cutoff from cached items, simplify reconcile
- When lastModified is missing but items exist (via updateItem()),
derive cutoff from max(item.updated_at) instead of falling back
to reconcile's return value. Eliminates the fallback branch.
- reconcile() now called purely for side effects; return value ignored.
- MAX_SYNC_PAGES guard checks needNextPageSync (not needNextPageFetch)
to avoid spurious warning when cutoff already stopped the loop.
- Add test for mixed pages (Renovate + non-Renovate PRs interleaved).
- Update derived-cutoff test for caches without lastModified.
* fix(github): advance PR cache watermark from unfiltered page
* fix(github): add comment clarifying MAX_SYNC_PAGES is a safety net
Sergei Zharinov