Show source-bound tasks and proposed checks in Studio #2523

Implement the bounded source-inspection portion of the UVAI video-to-tasks brief in PR #2522.

Acceptance criteria:

• Make Tasks the initial Studio output view and associate requirements with source timestamps, quotations, and acceptance checks by stable IDs.
• Validate the canonical pack digest before displaying or exporting tasks; hold malformed, mismatched, missing, or stale source evidence.
• Export source-bound proposed work as JSON, retaining blockers and explicit not-run/unverified statuses.
• Align home messaging with the available source-to-tasks workflow and preserve existing checkout.
• Pass the frontend suite and deployment checks. Record browser acceptance limitations explicitly.

This issue does not claim execution, verified generated products, or a measured under-60-minute build. Step Runner work remains separately tracked in #2489.