Update docs, fix Pygame window, and improve camera stage timing

tests/test_pipeline.py

@@ -45,8 +45,6 @@ class TestStageRegistry:
         assert "pygame" in displays
         assert "websocket" in displays
         assert "null" in displays
-        # sixel and kitty removed; should not be present
-        assert "sixel" not in displays
 
     def test_create_source_stage(self):
         """StageRegistry.create creates source stages."""