The seasonal membership form now allows adding spouses and children
directly during registration (not just selecting pre-existing ones).
New family members are created as actual spouse/child records and
included in the pricing calculation. The price preview API also
reflects inline additions in real-time.

All discounts work correctly with inline members:
- Parent + child <15: 500 EGP off
- Husband + wife: 1000 EGP off
- Family of 5+: 1000 EGP off
- No qualification: 10% off
- VAT applied on all amounts
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>