express app ignores `--app-dir` option from `shiny run` commandline

[arabidopsis]

py-shiny/shiny/_main.py

Line 318 in 82a83ee

app_path = Path(app_no_suffix).resolve()

I think this line should be augmented as something like:

  if app_dir is not None:
    app_path = (Path(app_dir) / app_no_suffix).resolve()
  else:
    app_path = Path(app_no_suffix).resolve()

The is_express_app test does use the app_dir value to find the actual express app so we get a file not found exception