* feat(settings): delete unused downloaded speech models
Add a Remove Model dropdown on the Speech Model page so whisper.cpp,
Whisper, and VOSK downloads can be deleted from Settings. The currently
selected model is marked in use and cannot be removed until you switch
away from it.
Fixes#650
* fix(settings): move unused model deletion below the picker
Unused downloads is its own group under the model info card. Only leftover
files appear, each with a Delete button. The group hides when empty.
* fix(settings): collapse unused downloads into an expander
Keep leftover models behind one row so a long list does not stretch the
Speech Model page. Expand to delete files one at a time; the list scrolls
once it grows past a few entries.
* fix(settings): keep leftover model list from clipping in the expander
Wrap the unused-downloads list so the expander can show a few rows and
scroll the rest, instead of painting only the first leftover.
