Set uwsm launch prefix automatically

### Feature Description

dms could set `DMS_DEFAULT_LAUNCH_PREFIX="uwsm-app -- "` if uwsm is detected (we already run `uwsm check is-active` somewhere else)

https://github.com/AvengeMedia/DankMaterialShell/blob/f2be6cfeb1c9a3a9546256817fc38fe661666ec5/core/cmd/dms/shell.go#L435-L437
(note: This block is there twice in shell.go)

Start in core/cmd/dms/shell.go around lines 435-437 and inspect both copies of this block. Read the existing uwsm check, then trace how DMS_DEFAULT_LAUNCH_PREFIX is used. Done means the prefix is set to "uwsm-app -- " when uwsm is detected and remains unchanged when it is not.

Written by the indexing model from the issue text.