Refactor environment and configuration management

- Updated the project structure to store configuration files (.env, models.yaml, extensions.yaml) in the project root instead of the user's home directory.
- Enhanced the setup process to automatically copy example files to the project root on first run.
- Implemented a migration function to transfer legacy configuration files from the user's home directory to the new project structure.
- Revised documentation to reflect changes in file locations and setup instructions.
- Improved code readability and maintainability by refactoring path management functions.

tests/conftest.py

@@ -1,4 +1,4 @@
-"""Keep tests from picking up a real ~/.gpu-rent/.env or OS_* from the shell."""
+"""Keep tests from picking up a real project .env or OS_* from the shell."""
 
 import pytest