docs(mcp): map operations to tools accurately

[qinyingran-TT]

Description

Correct the MCP mapping description in the Cart, Checkout, and Order MCP specifications and in the glossary.

The previous text stated that UCP capabilities map one-to-one to MCP tools. A capability can expose multiple operations, while each exposed operation is represented by one MCP tool. The revised wording reflects that relationship consistently across the documentation.

This is a documentation-only clarification. It does not change schemas, tool names, request or response formats, or runtime behavior.

Category (Required)

• 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

None.

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.

Validation performed:

• Relevant pre-commit hooks for the four changed Markdown files: passed.
• Documentation JSON examples: 30 passed, 0 failed.
• Strict MkDocs build with DOCS_MODE=spec: passed.
• Strict MkDocs build with DOCS_MODE=root: passed.

Unit tests were not run because this change only updates documentation wording.

Screenshots / Logs (if applicable)

N/A — wording-only documentation change.