Replaces 18 useCallback wrappers with a typed action union and
encounterReducer. Undo/redo wrapping is now systematic per-case in
the reducer instead of ad-hoc per operation. Complex cases (undo/redo,
bestiary add, player character add) are extracted into helper functions.
The stat block auto-show on bestiary add now uses lastCreatureId from
reducer state instead of the synchronous return value, with a useEffect
in use-action-bar-state to react to changes.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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