docs: add description for catalog fulfillment property

[carolinerg1]

Description

This change adds an explicit "description" to the Fulfillment property in "source/schemas/shopping/fulfillment.json" under "$defs.fulfillment_variant" and "$defs.fulfillment_lookup_variant".

Fixes an issue where the Properties table in the Fulfillment Extension specification (docs/specification/fulfillment.md), rendered dynamically via the {{ extension_fields(...) }} macro, displayed a blank description for the fulfillment property (Catalog Fulfillment).

Changes

• Updated source/schemas/shopping/fulfillment.json:
  • Added "description": "Fulfillment options and availability for this variant." to properties.fulfillment within fulfillment_variant.
  • Added "description": "Fulfillment options and availability for this variant." to properties.fulfillment within fulfillment_lookup_variant.

Category (Required)

Please select one or more categories that apply to this change.

• Core Protocol: Changes to the base communication layer, global context, or breaking refactors. (Requires Technical Council approval)
• Governance/Contributing: Updates to GOVERNANCE.md, CONTRIBUTING.md, or CODEOWNERS. (Requires Governance Council approval)
• Capability: New schemas (Discovery, Cart, etc.) or extensions. (Requires Maintainer approval)
• Documentation: Updates to README, or documentations regarding schema or capabilities. (Requires Maintainer approval)
• Infrastructure: CI/CD, Linters, or build scripts. (Requires DevOps Maintainer approval)
• Maintenance: Version bumps, lockfile updates, or minor bug fixes. (Requires DevOps Maintainer approval)
• SDK: Language-specific SDK updates and releases. (Requires DevOps Maintainer approval)
• Samples / Conformance: Maintaining samples and the conformance suite. (Requires Maintainer approval)
• UCP Schema: Changes to the ucp-schema tool (resolver, linter, validator). (Requires Maintainer approval)
• Community Health (.github): Updates to templates, workflows, or org-level configs. (Requires DevOps Maintainer approval)

Related Issues

Checklist

• I have followed the Contributing Guide (including Conventional Commits title requirements and ! for breaking changes).
• I have updated the documentation (if applicable).
• My changes pass all local linting and formatting checks.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• (For Core/Capability) I have included/updated the relevant JSON schemas.
• I have regenerated Python Pydantic models by running generate_models.sh under python_sdk.

Screenshots / Logs (if applicable)

Current Fulfillment with blank description:

Updated Fulfillment with a detailed description:

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[damaz91]

Great catch @carolinerg1 ! This table is indeed rendered poorly.

I found out that's not caused by something missing in the schema, but rather in the table rendering macro called in the wrong way.

Current: {{ extension_fields('fulfillment', 'fulfillment') }}

Correct: {{ extension_fields('fulfillment', 'checkout') }}

Opened #592 to fix. Thanks again!