Implement stat block panel fold/unfold and pin-to-second-panel

Replace the close button and heading with fold/unfold controls that
collapse the panel to a slim right-edge tab showing the creature name
vertically, and add a pin button (xl+ viewports with creature loaded)
that opens the creature in a second left-side panel for simultaneous
reference. Fold state is respected on turn change. 19 acceptance tests.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

specs/035-statblock-fold-pin/checklists/requirements.md

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+# Specification Quality Checklist: Stat Block Panel Fold/Unfold and Pin
+
+**Purpose**: Validate specification completeness and quality before proceeding to planning
+**Created**: 2026-03-11
+**Feature**: [spec.md](../spec.md)
+
+## Content Quality
+
+- [x] No implementation details (languages, frameworks, APIs)
+- [x] Focused on user value and business needs
+- [x] Written for non-technical stakeholders
+- [x] All mandatory sections completed
+
+## Requirement Completeness
+
+- [x] No [NEEDS CLARIFICATION] markers remain
+- [x] Requirements are testable and unambiguous
+- [x] Success criteria are measurable
+- [x] Success criteria are technology-agnostic (no implementation details)
+- [x] All acceptance scenarios are defined
+- [x] Edge cases are identified
+- [x] Scope is clearly bounded
+- [x] Dependencies and assumptions identified
+
+## Feature Readiness
+
+- [x] All functional requirements have clear acceptance criteria
+- [x] User scenarios cover primary flows
+- [x] Feature meets measurable outcomes defined in Success Criteria
+- [x] No implementation details leak into specification
+
+## Notes
+
+- All items pass. Spec is ready for `/speckit.clarify` or `/speckit.plan`.
+- The spec mentions "~200ms ease-out" which is a design constraint from the original issue, not an implementation detail — it describes the user-perceived behavior.
+- CSS animation timing is retained as a UX specification, not a technology choice.