fix(storyboard): emit unresolved_hidden_by_pagination meta-observation (#718)

[bokelley]

Summary

Closes #718. When refs_resolve sees target_paginated AND at least one ref was demoted to unresolved_with_pagination, the validator now emits a new unresolved_hidden_by_pagination meta-observation so graders can detect sellers indefinitely returning pagination.has_more: true to hide refs they can't service. Pass/fail semantics unchanged — graders interpret the flag.

Catches the integrity gap introduced by #717's pagination demotion: a seller that unconditionally returns has_more: true masks unresolved refs, and graders keying on refs_resolve.passed alone miss the structural smell. The new observation gives compliance dashboards an independent grader signal.

Design

Payload mirrors scope_excluded_all_refs: { kind, unresolved_count }. The per-ref detail already lives in the unresolved_with_pagination observations emitted immediately after — duplicating refs would inflate cap pressure without adding signal. unresolved_count is deduped so it matches the per-ref observation count.

Naming is neutral (unresolved_hidden_by_pagination) to match sibling observations (target_paginated, scope_excluded_all_refs, non_object_values_filtered). The validator names structural smells; graders decide intent.

Reviewer passes

Run through code-reviewer and ad-tech-protocol-expert. Feedback addressed:

• Renamed pagination_bypass_suspected → unresolved_hidden_by_pagination (protocol-expert: smuggles accusation into the observation shape; sibling observations are all neutral descriptors)
• Added 4th test pinning the dedup contract between unresolved_count and per-ref unresolved_with_pagination observations (code-reviewer)
• Changeset links adcp#2601 as the spec-level sunset condition (protocol-expert)

Test plan

• npm test — all suites pass
• node --test test/lib/storyboard-validations-refs-resolve.test.js — 43/43 pass (4 new)
  • emits on paginated+unresolved co-occurrence, passed stays true
  • does NOT emit when paginated but all refs resolve
  • does NOT emit when unresolved but not paginated
  • unresolved_count reports deduped refs, not raw occurrences

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