Version bump to 10.30.15 - Force PayPal tracking fix deployment

- Increment version from 10.30.14 to 10.30.15
- Update plugin header, SLN_VERSION constant, and readme stable tag
- Add changelog entry for PayPal payment tracking fix
- Force fresh deployment to ensure fixes are applied on remote server

This version bump is necessary to trigger a clean deployment of the
PayPal tracking fix that was not being applied despite successful pipeline runs.

Changes include:
- Explicit post_status during booking creation (prevents auto-draft default)
- Refined status protection filter to only apply to existing bookings
- Enhanced logging for debugging status transitions