build with uv rather than pip

The build command was `pip install .`, which is what the dora docs use because
`--uv` rewrites it. Spelling it `uv pip install .` means the dataflow never
installs through pip at all, whether or not `--uv` was passed. The cost is that
a node then needs a virtualenv to install into, so dataflows must be run with
`--uv`; AGENTS.md says so.

Note that the PR #3 branch still carries `pip install .`; landing this branch
on top of it is what corrects that.

README.md

@@ -16,7 +16,7 @@ nodes:
   - id: view
     git: ssh://git@gitea.liria.cl:5001/liria/dora-image-view.git
     tag: v0.1.0
-    build: pip install .
+    build: uv pip install .
     path: dora-image-view
     inputs:
       image: camera/image_bgr