roadmap_authority: project the accepted node id set from the frontier plan (#11310 successor)

[gunbai-bot]

Summary

• Adds gunbc.roadmap_authority accepted_node_ids_projection(history) → AcceptedNodeIdsProjected { ids } | AcceptedNodeIdsProjectionRefused { detail }. It is the accepted half of frontier_sets_projection and sits beside withheld_node_ids_projection.
• It is the successor to accepted_roadmap_node_ids_projection, which Add a Superseded revocation disposition; revoke the stranded entry-graph-union-construction receipt #11310 deleted. The difference is the reason for that deletion: the new projection reads the frontier plan, so a revoked, superseded or unreplayable history refuses. The old wrapper read the receipts alone and would not have refused.

Consumer (§3c)

gunb-ai/gunbc-private test.claim.strategy_witness public_accepted_roadmap_set is currently AcceptedSetUnavailable, and it names this deletion as its missing authority. That makes witness_capability_evidence_consistent_with_public_authority refuse by construction (second cause of the known-red row in strategy.private_witness_workflow). Its restoration trigger is "a public authority again projects the accepted roadmap node id set". This PR supplies that authority. Repointing the private witness is a follow-up in gunbc-private.

Evidence

Executed with gunbc run --claim-run on the test.claim.roadmap_receipt_continuity_acceptance entry:

• witness_accepted_projection_refuses_when_history_load_refuses: PASS. A refused load refuses with the same detail.
• witness_accepted_projection_matches_authority_projection_on_fixture_history: PASS. The set is nonempty and equals RoadmapAuthorityProjected.accepted over the same history.
• Mutation: projecting withheld in place of accepted makes the second witness FAIL. The mutation was then reverted.

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