Add JulyPlayersImportSeeder for OC-Sport legacy player data

Imports Team (99) and Academy (93) players from HTML sheet one at a time
using existing services (InvoiceService, PaymentService). Creates Person →
Participant → Enrollment → Invoice → Payment per player, with installment
plan attachment for partial القيد payments. Cross-sheet duplicates are
written to storage/app/july_import_duplicates.json. Idempotent by name.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>