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/README.md

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+# responsibility_attribution_negative
+
+Tests that thematic proximity, department discussion and objection do not create
+an action-item owner.
+
+The scenario includes a Marketing participant who comments critically on
+Business Development criteria. No one assigns that participant responsibility
+for defining the criteria, and the participant does not accept such a task.
+
+Expected behavior:
+
+- Do not assign Business Development criteria to the Marketing participant.
+- Do not reclassify the Marketing participant as Business Development.
+- Preserve the objection as a position.
+- Keep responsibility open unless explicitly assigned.