fix: resolve 6 pre-ship audit bugs

- Webhook entry identifier: use entry GUID instead of feed identifier
- Optimistic rollback: add previousTimeline snapshot and onError handler
  to both useToggleEntryReadState and useToggleEntrySavedState
- Rate limiter memory leak: delete Map entries when window expires,
  use else-if to avoid re-setting after delete
- Entries API limit param: use Number.isFinite guard instead of falsy
  coercion that treats 0 as default
- PWA manifest: add PNG raster icon routes (192x192, 512x512) for
  devices that don't support SVG icons
- Billing webhook: throw on DB errors and return 500 so Stripe retries
  failed events instead of silently losing them

0 files changed, 0 insertions, 0 deletions