`dora validate` matches a node manifest to a `path:` node by entrypoint. With
no manifest beside examples/source.py the root dora-node.yml was tried against
it, did not match its entrypoint, and warned -- which `strict_types: true`
turns into a non-zero exit, failing CI.
Declaring the source's output types in the new manifest rather than as
`output_types:` in dataflow.yml is also what makes them checked: an inline
annotation shadows the manifest, so the manifest would be injected but never
compared against the viewer's.
Verified with dora-cli 1.0.1: validate passes with both contracts injected, and
`CI=true SOURCE_FRAMES=30 dora run dataflow.yml --uv` runs both nodes to a
clean exit.
