fix: only delete individual LoRA file instead of entire parent directory (#8954)

When deleting a file-based model (e.g. LoRA), the previous logic used
rmtree on the parent directory, which would delete all files in that
folder — even unrelated ones. Now only the specific model file is
removed, and the parent directory is cleaned up only if empty afterward.

invokeai/app/services/model_install/model_install_default.py

@@ -663,10 +663,12 @@ class ModelInstallService(ModelInstallServiceBase):
         # directory. However, the path we store in the model record may be either a file within the key directory,
         # or the directory itself. So we have to handle both cases.
         if model_path.is_file() or model_path.is_symlink():
-            # Sanity check - file models should be in their own directory under the models dir. The parent of the
-            # file should be the model's directory, not the Invoke models dir!
-            assert model_path.parent != self.app_config.models_path
-            rmtree(model_path.parent)
+            # Delete the individual model file, not the entire parent directory.
+            # Other unrelated files may exist in the same directory.
+            model_path.unlink()
+            # Clean up the parent directory only if it is now empty
+            if model_path.parent != self.app_config.models_path and not any(model_path.parent.iterdir()):
+                model_path.parent.rmdir()
         elif model_path.is_dir():
             # Sanity check - folder models should be in their own directory under the models dir. The path should
             # not be the Invoke models dir itself!