MCP: improve recommendation precision and caching

[adierkens]

Summary

• add composition-aware component recommendations with grouped semantic matching
• preserve documented internal-only pattern support for all-source callers
• cache bounded pattern enrichment and exact-input final CSS validation
• keep existing MCP schemas and single-icon behavior unchanged

Validation

• focused MCP tests pass (51/51)
• npm run type-check -w @primer/mcp
• npm run build -w @primer/mcp

Privacy and scope review

• stacked on MCP: federate documented internal components #8230
• no session identifiers, private eval findings, local paths, or unrelated public API additions
• gitleaks and independent full-range publication review passed

This is a draft canary for evaluation before merge.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 90435ca

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes changesets to release 1 package

Name	Type
@primer/mcp	Minor

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[github-actions]

⚠️ Action required

👋 Hi, this pull request contains changes to the source code that github/github-ui depends on. If you are GitHub staff, test these changes with github/github-ui using the integration workflow. Check the integration testing docs for step-by-step instructions. Or, apply the integration-tests: skipped manually label to skip these checks.