fix(rest/python): emit schema-valid shipping events

[FanouZeng-TT]

Description

ship_order persisted fulfillment events with a non-schema timestamp field and omitted the required occurred_at and line_items fields. Orders returned after simulated shipping therefore failed validation against the generated Order model.

Fix: emit occurred_at and an event line-item projection containing each order line-item ID and total quantity. The integration test exercises the public simulation endpoint and validates the resulting order with Order.model_validate.

Category (Required)

• Core Protocol
• Governance/Contributing
• Capability
• Documentation
• Infrastructure
• Maintenance
• SDK
• Samples / Conformance
• UCP Schema
• Community Health (.github)

Related Issues

N/A

Checklist

• I have followed the Contributing Guide and Code of Conduct.
• I have updated the documentation (if applicable).
• My changes pass all local linting and formatting checks.
• I have added tests that prove the fix is effective.
• New and existing unit tests pass locally with my changes.
• I have included/updated the relevant JSON schemas (Core/Capability only).
• I have regenerated Python Pydantic models (not applicable).

Screenshots / Logs (if applicable)

• Python server test suite: 137 passed
• pre-commit run --all-files: passed