Phase 2: Entity data model extensions for behavior system

- Add Behavior enum (IDLE..FLEE, 11 values) and Trigger enum (DONE,
  BLOCKED, TARGET) as runtime IntEnum classes (closes #297, closes #298)
- Add entity label system: labels property (frozenset), add_label(),
  remove_label(), has_label(), constructor kwarg (closes #296)
- Add cell_pos integer logical position decoupled from float draw_pos;
  grid_pos now aliases cell_pos; SpatialHash::updateCell() for cell-based
  bucket management; FOV/visibility uses cell_position (closes #295)
- Add step callback and default_behavior properties to Entity for
  grid.step() turn management (closes #299)
- Update updateVisibility, visible_entities, ColorLayer::updatePerspective
  to use cell_position instead of float position

BREAKING: grid_pos no longer derives from float x/y position. Use
cell_pos/grid_pos for logical position, draw_pos for render position.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/SpatialHash.h

@@ -33,7 +33,11 @@ public:
     // This removes from old bucket and inserts into new bucket if needed
     void update(std::shared_ptr<UIEntity> entity, float old_x, float old_y);
 
-    // Query all entities at a specific cell (exact integer position match)
+    // Update entity position using integer cell coordinates (#295)
+    // Removes from old bucket and inserts into new based on cell_position
+    void updateCell(std::shared_ptr<UIEntity> entity, int old_x, int old_y);
+
+    // Query all entities at a specific cell (uses cell_position for matching)
     // O(n) where n = entities in the bucket containing this cell
     std::vector<std::shared_ptr<UIEntity>> queryCell(int x, int y) const;