CUDA single lock

Circumvent issues with https://github.com/prefix-dev/pixi/issues/1051 and declare a single manifest that also contains CUDA environment support.

doc/install.rst

@@ -61,7 +61,9 @@ Choose the relevant tab for details on each of those installation paths.
       pixi install --frozen --environment cuda
       pixi run -e cuda mednet info
 
-   Refer to further pixi configuration tips on the *Development* tab above.
+   To enable CUDA support, always run applications using the ``cuda``
+   environment via ``pixi run -e cuda ...``.  Refer to further pixi
+   configuration tips on the *Development* tab above.
 
 
 .. _mednet.setup: