add an in-repo synthetic source so the example needs no network

The example dataflow pulled opencv-video-capture and pyarrow-sender from
dora-hub, needed a webcam, and left `bbox` unwired because every bbox source
is a detector. examples/source.py emits an animated frame, the box around the
square in it, and a caption, so the dataflow exercises all three inputs with
nothing outside this checkout.

SOURCE_FRAMES bounds the run, which lets CI run the dataflow headless rather
than only validate it. Drops the dora-zed and dora-yolo wirings from the
README and trims AGENTS.md to what the code and README do not already say.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018WLVZCFFcCH1EpTXGfS9aD

dataflow.yml

@@ -1,41 +1,34 @@
-# The repository's own example: a webcam and a fixed caption feeding the viewer.
-# The plot node is built from this checkout with `path:` + `build:`, so
-# `dora validate` picks up the typed contract in dora-node.yml next to it.
+# The repository's own example, and its end-to-end test: a synthetic source
+# feeding the viewer. Everything it needs is in this checkout -- no camera, no
+# detector, no network -- so it is also what CI runs.
 #
-# Run it with `--uv` so every Python node gets its own managed environment.
-# A consumer wires the node from a tag instead — see README.md.
+# Both nodes are built from the checkout with `path:` + `build:`, which is what
+# lets `dora validate` pick up the typed contract in dora-node.yml. A consumer
+# wires the viewer from a tag instead -- see README.md.
 #
-# `bbox` is left unwired: every bbox source is a detector, and pulling one in
-# would put a model download in the way of a webcam preview. README.md shows
-# the wiring.
+# Run it with `--uv` so every node gets its own managed environment.
 strict_types: true
 
 nodes:
-  - id: camera
-    git: https://github.com/dora-rs/dora-hub.git
-    build: pip install ./node-hub/opencv-video-capture
-    path: opencv-video-capture
+  - id: source
+    path: examples/source.py
+    # The source needs dora-rs, numpy and pyarrow; installing the project gives
+    # it exactly the versions pinned in uv.lock.
+    build: pip install .
     inputs:
-      tick: dora/timer/millis/100
+      tick: dora/timer/millis/33
     outputs:
       - image
+      - bbox
+      - text
     output_types:
       image: std/core/v1/UInt8
-
-  - id: caption
-    git: https://github.com/dora-rs/dora-hub.git
-    build: pip install ./node-hub/pyarrow-sender
-    path: pyarrow-sender
-    env:
-      DATA: "'dora-plot'"
-    outputs:
-      - data
-    output_types:
-      data: std/core/v1/String
+      text: std/core/v1/String
 
   - id: plot
     path: dora-plot
     build: pip install .
     inputs:
-      image: camera/image
-      text: caption/data
+      image: source/image
+      bbox: source/bbox
+      text: source/text