Enforce explicit responsibility attribution

- document responsibility attribution as a project-wide invariant
- prevent inferred ownership in protocol rendering
- add negative gold regression for false responsibility assignment
- document future responsibility evidence and attribution model
- record the real-life benchmark finding

tests/gold/responsibility_attribution_negative/transcript.txt

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+Mara: For the new partner intake, we still need criteria for Business Development projects.
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+Noah: From Marketing, I can tell you that generic criteria will not work. A digital campaign and a physical product launch need different checks.
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+Mara: Right, so the Business Development criteria remain open.
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+Noah: I am not taking that on. I only want to flag that the criteria cannot be generic.
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+Lea: Then we should keep the owner open until Business Development confirms who will define them.
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+Mara: Agreed. Responsibility stays open for now, and we will ask Business Development for an owner.