add a depth map panel

The node showed a colour image only, so debugging a depth pipeline meant
either trusting the numbers or writing a throwaway viewer. It now keeps one
panel per frame stream -- image and depth -- and tiles them side by side,
scaled to a common height. Wiring one is a plain viewer; wiring both shows
them together. bbox and text stay overlays rather than panels.

The contract follows what dora-zed already publishes: float32 [H, W] in
millimetres with 0 for missing. It is sent there as a raw byte slice, so the
payload arrives as UInt8 despite the Float32 contract and is reinterpreted
rather than converted.

Auto-ranging the colormap over the valid pixels' full extent, rather than over
a percentile of them, is deliberate and was not the first attempt: trimming
the tails collapsed on the scene the node exists for. A small object in front
of a large wall is a few percent of the pixels, so both tails landed on the
wall and the object clipped away. Rendering a frame and looking at it found
that; every test passed either way.

Verified with dora-cli 1.0.1: validate passes with both contracts injected,
the dataflow runs both nodes to a clean exit, and a composed frame was
rendered and inspected.

dora-node.yml

@@ -7,9 +7,9 @@
 apiVersion: 1
 name: dora-image-view
 namespace: liria
-description: Overlays bounding boxes, labels, and text on an image input and displays it in an OpenCV window
+description: Displays an image and a depth map side by side in an OpenCV window, with bounding box and text overlays
 categories: [visualization, debug]
-keywords: [opencv, view, bbox, bounding-box, image, visualization, object-detection]
+keywords: [opencv, view, bbox, bounding-box, image, depth, visualization, object-detection]
 
 runtime: python
 entrypoint: dora-image-view
@@ -41,10 +41,26 @@ inputs:
     description: >-
       Text string to overlay at the top-left corner. Stored and drawn on the
       next image redraw.
+  depth:
+    type: std/core/v1/Float32
+    required: false
+    description: >-
+      Depth map as a flat Float32 buffer, described by the metadata
+      {shape: [height, width], units}. Millimetres unless `units` says `m`;
+      0 and non-finite values are missing depth and draw black. Colour-mapped
+      into its own panel, which receiving this input redraws.
 
 outputs: {}
 
 env:
+  VIEW_DEPTH_MIN_MM:
+    type: float
+    description: >-
+      Pin the near end of the depth colour range, in millimetres. Each end is
+      auto-ranged over the valid pixels of the current frame when it is unset.
+  VIEW_DEPTH_MAX_MM:
+    type: float
+    description: Pin the far end of the depth colour range, in millimetres.
   VIEW_WIDTH:
     type: int
     description: Resize the displayed frame to this width (pixels). Defaults to the image input width.
@@ -59,6 +75,7 @@ example: |
     build: pip install .
     path: dora-image-view
     inputs:
-      image: camera/image
+      image: camera/image_bgr
+      depth: camera/depth
       bbox: detector/bbox
       text: detector/text