refactor(payment): centralize payment methods resolution

[hackmanser]

Closes #4927.

Summary

Centralize payment-method availability resolution into PaymentMethodsResolver and reuse it in API + checkout + selection endpoint.

Changes

• Add AppBundle\Payment\PaymentMethodsResolver + ResolvedPaymentMethod.
• Use resolver in src/Action/Order/PaymentMethods.php and src/Form/Checkout/CheckoutPaymentType.php.
• Validate payment-method selection against resolver to prevent selecting unavailable methods.
• Add unit tests for resolver behavior.

Notes

• apple_pay/google_pay remain API-only (not shown in checkout form).
• Pawapay: card is excluded when the restaurant has Pawapay disabled.

Testing

• docker compose run --rm php vendor/bin/phpunit --filter PaymentMethodsResolverTest

CI (fork)

• Lint JS: https://github.com/hackmanser/coopcycle-web/actions/runs/21802162859
• Lint PHP: https://github.com/hackmanser/coopcycle-web/actions/runs/21802162858
• Unit Tests (PHP): https://github.com/hackmanser/coopcycle-web/actions/runs/21802162872
• Review PR: Refactor payment methods resolution hackmanser/coopcycle-web#4

[alexsegura]

@hackmanser why did you close it?