fix: make --input-path optional for import/export commands

otherwise `--list-models` won't work without the input path, and
that's just annoying

src/wuttasync/cli/base.py

@@ -255,7 +255,7 @@ def file_import_command_template(
                          exists=True, file_okay=True, dir_okay=True,
                          help="Path to input file(s).  Can be a folder "
                          "if app logic can guess the filename(s); "
-                         "otherwise must be complete file path.")] = ...,
+                         "otherwise must be complete file path.")] = None,
 
 ):
     """