refactor: split the opencv-plot viewer into its own dataflow

dataflow.yml is now the camera alone, so running it no longer pulls
dora-hub over pip or needs a display. dataflow_plot.yml adds the viewer
on image_bgr for when the stream should be looked at.

dora 1.0 resolves an input's source only within the same descriptor, so
the camera node is declared in both files rather than shared, and the two
are run one at a time. CI validates both, which is what catches an output
rename that breaks only the viewer.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01A65jaxrPXMN9EhBDMmMWb2

dataflow.yml

@@ -1,6 +1,9 @@
 # The repository's own example: builds and runs the node from this checkout, so
 # `dora validate` picks up the typed contract in dora-node.yml next to it.
 # A consumer wires the node from a tag instead — see README.md.
+#
+# The camera alone, with no viewer and no Python dependency. For a run that
+# also displays the stream, use dataflow_plot.yml.
 strict_types: true
 
 nodes:
@@ -15,10 +18,3 @@ nodes:
       - point_cloud
       - camera_info
       - camera_state
-
-  - id: plot
-    git: https://github.com/dora-rs/dora-hub.git
-    build: pip install ./node-hub/opencv-plot
-    path: opencv-plot
-    inputs:
-      image: zed-camera/image_bgr