refactor: rename the node from opencv-plot to dora-plot

The repository is dora-plot, but the package, the entrypoint, the manifest
name and the window title were all opencv-plot. Consumers wire the node by
`path:`, so the split name was visible in every dataflow.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018WLVZCFFcCH1EpTXGfS9aD

tests/test_dora_plot.py

@@ -7,8 +7,8 @@ import numpy as np
 import pytest
 from PIL import Image
 
-from opencv_plot import bbox, decode
-from opencv_plot.plot import Bboxes, Plot
+from dora_plot import bbox, decode
+from dora_plot.plot import Bboxes, Plot
 
 WIDTH, HEIGHT = 12, 8