feat(ai): add parallel delivery workflow

[Dmitryaf]

Summary

• Add an optional parallel-delivery workflow and a short task-contract template.
• Define writer isolation, shared-contract ownership, integration, and cleanup boundaries.
• Expose prompt parallel through the existing CLI and sync catalog without changing manifest or lock schema versions.
• Cover explicit workflow selection, prompt rendering, synchronization, and compatibility in tests.

Local validation

• scripts/check-hub.ps1 passed.
• tests/test-tooling.ps1 passed (426 assertions in the integration suite).
• git diff --check passed.

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