Connect to pipewire/jack default output automatically

The logic to connect JACK output ports is here: https://github.com/agraef/purr-data/blob/master/pd/src/s_audio_jack.c#L171

This doesn't work with pipewire-jack as there is no output named 'system'.

It would be great if JACK backend autoconnected the output and input ports to the default audio outputs and inputs. Maybe this requires setting some attribute so the Pipewire session manager takes care of it - I don't yet know.

Start at pd/src/s_audio_jack.c around line 171, where the JACK output-port connection logic is located. Investigate how pipewire-jack exposes default audio inputs and outputs, including whether a session-manager attribute is needed. Done means the JACK backend automatically connects both output and input ports to the default devices.

Written by the indexing model from the issue text.