add a depth output

Publish sl::MEASURE::DEPTH as float32 [H, W] millimetres on every frame that
carries image_bgr, with the intrinsics, frame_id and timestamps the other
outputs carry.

The map is copied out rather than published in place: sl::Mat rows can be
padded, so the buffer is not necessarily H * W floats. inf and nan are cleared
to 0 in the same pass, matching the reference driver — a hole is meaningful and
a consumer cannot back-project a non-finite value.

Consumers that need 3D can now back-project depth with the published
intrinsics instead of receiving a point cloud.

Also drops the stale objects entry from the dataflow outputs, missed when
detection was removed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Y7g2cBJ5e3r15ZbJ9WZn8c

dataflow.yml

@@ -8,7 +8,9 @@ nodes:
       tick: dora/timer/millis/100
     outputs:
       - image_bgr
-      - objects
+      - depth
+      - point_cloud
+      - camera_info
 
   - id: plot
     git: https://github.com/dora-rs/dora-hub.git