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>

tests/unit/entity_labels_test.py

@@ -0,0 +1,75 @@
+"""Unit test for #296: Entity label system."""
+import mcrfpy
+import sys
+
+def test_labels_crud():
+    """Basic add/remove/has operations."""
+    e = mcrfpy.Entity()
+    assert len(e.labels) == 0, "New entity should have no labels"
+
+    e.add_label("solid")
+    assert e.has_label("solid"), "Should have 'solid' after add"
+    assert not e.has_label("npc"), "Should not have 'npc'"
+
+    e.add_label("npc")
+    assert len(e.labels) == 2
+
+    e.remove_label("solid")
+    assert not e.has_label("solid"), "Should not have 'solid' after remove"
+    assert e.has_label("npc"), "'npc' should remain"
+    print("PASS: labels CRUD")
+
+def test_labels_frozenset():
+    """Labels getter returns frozenset."""
+    e = mcrfpy.Entity()
+    e.add_label("a")
+    e.add_label("b")
+    labels = e.labels
+    assert isinstance(labels, frozenset), f"Expected frozenset, got {type(labels)}"
+    assert labels == frozenset({"a", "b"})
+    print("PASS: labels returns frozenset")
+
+def test_labels_setter():
+    """Labels setter accepts any iterable of strings."""
+    e = mcrfpy.Entity()
+    e.labels = ["x", "y", "z"]
+    assert e.labels == frozenset({"x", "y", "z"})
+
+    e.labels = {"replaced"}
+    assert e.labels == frozenset({"replaced"})
+
+    e.labels = frozenset()
+    assert len(e.labels) == 0
+    print("PASS: labels setter")
+
+def test_labels_constructor():
+    """Labels kwarg in constructor."""
+    e = mcrfpy.Entity(labels={"solid", "npc"})
+    assert e.has_label("solid")
+    assert e.has_label("npc")
+    assert len(e.labels) == 2
+    print("PASS: labels constructor kwarg")
+
+def test_labels_duplicate_add():
+    """Adding same label twice is idempotent."""
+    e = mcrfpy.Entity()
+    e.add_label("solid")
+    e.add_label("solid")
+    assert len(e.labels) == 1
+    print("PASS: duplicate add is idempotent")
+
+def test_labels_remove_missing():
+    """Removing non-existent label is a no-op."""
+    e = mcrfpy.Entity()
+    e.remove_label("nonexistent")  # Should not raise
+    print("PASS: remove missing label is no-op")
+
+if __name__ == "__main__":
+    test_labels_crud()
+    test_labels_frozenset()
+    test_labels_setter()
+    test_labels_constructor()
+    test_labels_duplicate_add()
+    test_labels_remove_missing()
+    print("All #296 tests passed")
+    sys.exit(0)