No channel isolation — the env you get depends on the user's conda config

[LouieSlocombe]

environment.yml lists conda-forge but has no nodefaults. On my machine (global config: channels: [defaults], channel_priority: flexible)

I had to force CONDA_CHANNEL_PRIORITY=strict to match CI. A user following the README verbatim gets a mixed-channel env; CI does not, because it sets channel-priority: strict and conda-remove-defaults: true.

Fix: add - nodefaults to the channels list so the file is self-contained regardless of user config.