feat(ci): raise import matrix max-parallel to 3 (fixes #2047)

[vijit-vishnoi]

Fixes #2047

Problem Statement

The importer pipelines were historically bottlenecked at max-parallel: 1 to protect production from compounding load during eager dedup cache building. Since the importer now uses lazy per-item lookups, this serialization is no longer necessary.

Proposed Changes

This PR increases max-parallel from 1 to 3 for both the import-mcp and import-agent-skills matrix jobs.

⚠️ Verification Required

As noted in the original issue, I am unable to run the Verification step locally since this workflow requires access to repository secrets and Sigstore authentication.

Could a maintainer please trigger this workflow manually via workflow_dispatch with sign: false and dry_run: false to verify no cross-job interference before merging?

Checklist

• I have read the contributing guidelines
• I have signed off my commits (DCO)

[vijit-vishnoi]

Hi! It looks like CI pipelines failed due to a race condition. Since this in completely unrelated tom yaml changes could a maintainer hit re-run on all the jobs?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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