fix: remove mise python venv config to silence warnings (#2879)
mise was configured to auto-activate a Python virtualenv at .venv, but since
this project uses uv for Python management the venv often doesn't exist. This
caused mise to print a warning on every new shell:
mise WARN no venv found at: .../.venv
Removing the config stops the warning. The project continues to use uv for
Python environment management via mise tasks.
