Phase 2: add hosted platform extension seams

[Verma-Punit]

Summary

• add configuration-driven seeder extension points for hosted distributions
• harden API login against cross-tenant authentication
• share billing, country, styling, factory, and scheduler behavior with the hosted platform
• add coverage for local country data

Verification

• php artisan test --compact (83 tests, 365 assertions)
• npm run build
• vendor/bin/pint --dirty --format agent