fix: resolve order endpoint from discovered UCP profile

[ShuoRen-TT]

Summary

Fixes #42.

Order conformance tests now resolve /orders/{id} through the discovered UCP shopping service endpoint instead of calling the test server base URL directly.

What changed

• Added IntegrationTestBase.get_order_url(order_id) as the order-resource equivalent of get_shopping_url(...).
• Updated order_test.py GET and PUT calls for /orders/{id} to use the discovered shopping service endpoint.

Why

The shopping REST spec says operation paths are relative to the merchant-provided endpoint from /.well-known/ucp under services["dev.ucp.shopping"][transport=rest].endpoint. Checkout tests already follow this pattern through get_shopping_url(...), but order tests were still using the root server_url, which fails for implementations that mount the shopping service below a path prefix.

Validation

• uv run ruff format --check integration_test_utils.py order_test.py
• uv run ruff check integration_test_utils.py order_test.py
• uv run python -m py_compile integration_test_utils.py order_test.py
• Smoke-checked get_order_url(...) with discovered endpoints both with and without a trailing slash.

I also attempted to run order_test.py against the local Flower Shop sample server. The server failed to start before conformance tests ran due to an existing local samples/python-sdk import mismatch: ImportError: cannot import name 'Checkout' from 'ucp_sdk.models.schemas.shopping.ap2_mandate.

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[ShuoRen-TT]

Hi maintainers, CLA is now passing and this PR is ready for review.

By way of introduction, we are an engineering team from TikTok currently working on UCP adoption together with merchants and ecosystem partners, including Shopify. As we go through real integration work, we expect to contribute fixes, conformance improvements, sample updates, and implementation feedback back to the UCP open source community.

This PR is intentionally small: it fixes #42 by making the order conformance tests resolve /orders/{id} through the discovered dev.ucp.shopping REST endpoint, matching the endpoint-resolution pattern already used by the checkout tests.

Could someone from devops-maintainers or above please take a look when you have a chance?

[carolinerg1]

Welcome to the community! Thank you so much for your contribution.

Could you please update your PR to follow the following format for the title: https://github.com/Universal-Commerce-Protocol/.github/blob/main/CONTRIBUTING.md#pull-request-titles-and-commit-messages

Also, it looks like you are using CODEX, please take a look at this to improve CODEX on UCP: https://github.com/Universal-Commerce-Protocol/ucp/blob/main/AGENTS.md

[ShuoRen-TT]

Welcome to the community! Thank you so much for your contribution.

Could you please update your PR to follow the following format for the title: https://github.com/Universal-Commerce-Protocol/.github/blob/main/CONTRIBUTING.md#pull-request-titles-and-commit-messages

Also, it looks like you are using CODEX, please take a look at this to improve CODEX on UCP: https://github.com/Universal-Commerce-Protocol/ucp/blob/main/AGENTS.md

Thanks for the welcome and the pointers!

I've updated the PR title to follow the Conventional Commits format and reviewed the UCP AGENTS.md guidance for AI-assisted contributions.

The remaining conformance CI failure appears to come from the Flower Shop sample server startup issue tracked in Universal-Commerce-Protocol/samples#118. I opened Universal-Commerce-Protocol/samples#119 to fix that SDK import mismatch. Once that lands, I can rerun this PR's conformance check.