add update_vocabulary dora input for runtime label changes

The open_vocab engine now accepts an update_vocabulary input event
carrying a UTF-8 comma-separated label string. Labels are re-encoded
immediately via the CLIP text encoder; the next tick uses the new
vocabulary. ZedNative ignores the input via a no-op base class method.

dataflow.yml

@@ -5,6 +5,7 @@ nodes:
     path: bin/dora_zed
     inputs:
       tick: dora/timer/millis/100
+      # update_vocabulary: vocabulary-node/labels  # optional: send new comma-separated labels at runtime
     outputs:
       - image_bgr
       - point_cloud