Fixes#30451.
In a case that both `--help-center` and `--help-center-dev-server`
flags are passed to `run-dev`, `--help-center` flag will take
precedence without throwing any error.
We also add a script called `build-help-center` that is required
to build the starlight documentation. If the `help-beta/dist` dir
is not present, `run-dev` will show an error message but will not
fail.
The returns plugin hasn’t been updated for mypy ≥ 1.6. This
annotation is more limited in that it only supports a fixed number of
positional arguments and no keyword arguments, but is good enough for
our purposes.
Signed-off-by: Anders Kaseorg <anders@zulip.com>
This makes no immediate reloads the default for runtornado, matching
the production configuration, and changes the development incantation
to be the one to specify the departure from the norm, with
--immediate-reloads.
