* Update Install Scripts
Add SPDX AGPL-3.0 headers to the installer scripts and let the piped web
installs take their common options from the environment.
- install.sh / install.ps1: read UNSLOTH_NO_TORCH (and UNSLOTH_PYTHON for
install.sh) so a piped install needs no positional flags. Flags and the
pipe forms still work; an explicit flag wins.
- Fix the UNSLOTH_STUDIO_HOME example so the variable sits after the pipe
and reaches sh instead of curl.
- Add SPDX headers to install.sh, install.ps1, the uninstall scripts, and
the MLX install scripts.
- Drop the internal test package names from the studio install comments.
* Mirror UNSLOTH_PYTHON env var to install.ps1
install.ps1 now reads UNSLOTH_PYTHON to pin the Python version, matching
install.sh, and lists all three env vars (UNSLOTH_NO_TORCH, UNSLOTH_PYTHON,
UNSLOTH_STUDIO_HOME) in the header examples. The requested version is
preferred during detection and used as the winget install target; behavior
is unchanged when the variable is unset.