fix(rest/nodejs): include line items in shipped events

[FanouZeng-TT]

Summary

• Populate Node shipped fulfillment events with the shipped order line item ids and quantities instead of an empty array.
• Add a fulfillment regression test that completes a checkout, ships its order, and verifies the event line item projection.

Test plan

• npm --prefix rest/nodejs test
• npm --prefix rest/nodejs run build
• uvx --directory . pre-commit run --files rest/nodejs/src/api/checkout.ts rest/nodejs/test/fulfillment.test.ts
• git diff --check