add typed Arrow payloads and a dora-image-view dataflow

dora-image-view takes std/media/v1/Image, and dora's compatibility graph
has no edge from std/core/v1/UInt8 to it, so wiring the two failed
`dora validate` whatever the node actually sent. Its flat-buffer fallback
would not have decoded these frames either: it reads width/height
metadata, and this node only published shape.

image and depth now go out as the Image struct, camera_info and
point_cloud as Float32 arrays and camera_state as a string, all built
against the Arrow C data interface in src/arrow so the node still links
no Arrow C++. Shape, dtype and encoding metadata are dropped where the
payload describes itself; intrinsics, frame_id and both timestamps are
unchanged. tests/run.sh covers the packing without a camera or the SDK,
round-tripping each array through pyarrow and rebuilding it under the
sanitizers.

Breaking: image_bgr is renamed to image and every payload changes shape.
dataflow_plot.yml is replaced by dataflow_view.yml, which wires the
viewer from a tag and repeats its contract in input_types so validate
checks both sides of the wiring.

dataflow.yml

@@ -3,7 +3,7 @@
 # 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.
+# also displays the stream, use dataflow_view.yml.
 strict_types: true
 
 nodes:
@@ -13,7 +13,7 @@ nodes:
     inputs:
       tick: dora/timer/millis/100
     outputs:
-      - image_bgr
+      - image
       - depth
       - point_cloud
       - camera_info