Allow Windows users to choose the Python environment location instead of always using the C: drive

Problem

On Windows, the installer always creates the Python environment on the system drive (C:), typically under the user's profile (AppData).

This is problematic for users who:

keep the system partition small (e.g. 100–150 GB),
have a dedicated SSD/HDD for development or AI workloads,
want to avoid filling the system drive with Python packages and dependencies.

Since the embedded Python environment and installed packages can grow significantly over time, forcing everything onto C: is inconvenient.

Expected behavior

During installation, allow the user to:

choose the location of the Python environment, or
specify a custom installation directory (for example D:\ComfyUI\python), or
respect an environment variable or command-line argument that overrides the default location.
Benefits
Prevents unnecessary usage of the system drive.
Makes installations more flexible for multi-drive systems.
Better matches common Windows software installation practices.
Helps users with limited free space on C:.

I think this would improve the Windows installation experience without affecting existing users, since the current behavior could remain the default.

Start by locating the Windows installer flow that creates the embedded Python environment and determine how its default location is selected. Done means a fresh Windows installation can select or override the environment directory while existing installations retain the current default behavior.

Written by the indexing model from the issue text.