fix(ui): reuse Home picker for Sound expansion (#12790)

* fix(ui): reuse Home picker for Sound expansion

Use the shared model chip and listbox for Sound expansion instead of
a native select. Keep explicit Sound selection and Backend default
independent from Home model preferences.

Preserve keyboard navigation and expose the selected value through an
accessible description. Hide runtime badges without loaded-model data.

Assisted-by: nib:gpt-6.1-sol
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

* test(ui): select Sound expansion through shared picker

Update media history coverage to use the model button and listbox.

Assisted-by: nib:gpt-6.1-sol
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

---------

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Co-authored-by: Ettore Di Giacinto <mudler@localai.io>

docs/content/features/text-to-audio.md

@@ -1170,7 +1170,10 @@ tool call, multiple calls, or invalid arguments returns a request error. Expansi
 Cancellation propagates to model loading, text inference, and audio generation.
 
 In **Studio → Sound → Simple**, choose a **Prompt expansion model** before
-submitting. The list contains installed, enabled chat models. **Backend default**
+submitting. Sound uses the same model picker as Home, with search for longer
+model lists and keyboard navigation. The list contains installed, enabled chat
+models. You must explicitly choose a model or **Backend default**; opening or
+dismissing the picker does not select a model. **Backend default**
 omits `expansion_model` and uses the audio backend's existing prompt behavior.
 Sound remembers either choice in this browser, separately from your chat model.
 If a remembered model disappears or loses chat support, choose again.