Add .gitignore and remove cached files

.backend

-vulkan

.gitignore

+# Backend selection file
+.backend
+
+# Virtual environments
+venv/
+.venv/
+env/
+
+# Python cache
+__pycache__/
+*.pyc
+*.pyo
+*.pyd
+.Python
+
+# Debug logs
+debug.log