Add actor sheet implementation using Foundry VTT v13 ApplicationV2 API:
- Base actor sheet class with tab navigation, drag-drop, scroll preservation
- Character sheet with header, main tab (stats, saves, skills, attacks)
- NPC sheet structure (templates only, styling pending)
- Resource bars with fill effect and backdrop pills for legibility
- Responsive layout using CSS Container Queries
- Fix for ApplicationV2 tab switching (cleanup stale parts)
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
