Fix cash pickup checkout without delivery quote

[roncodes]

Summary

• allow cash checkout initialization to receive no delivery service quote
• persist a null service quote for pickup while preserving subtotal and cash-on-delivery state
• add a regression test for cash pickup without a delivery quote

Verification

• complete Storefront server unit suite passes
• checkout boundary suite: 47 tests, 272 assertions
• PHP-CS-Fixer reports no changes
• git diff check passes

API and review notes

This aligns the implementation with the existing pickup checkout contract and does not add request fields. Cash checkout behavior requires human review before merge.

Static analysis baseline

The repository type command is currently blocked by its existing configuration and the touched controller has extensive pre-existing PHPStan findings. This PR does not expand scope into that baseline cleanup.