feat(audio): release/refresh output-device button (#263)

After bit-perfect ALSA Direct grabs a DAC exclusively (hw: + D-Bus
reservation), the device stays sequestered and is invisible to PipeWire,
so switching back to the PipeWire backend can't see it without restarting
the app. Tauri had a refresh affordance for hot-plugged DACs; this is the
refresh plus an explicit release, in one button.

Backend: Player::release_device() / AudioCommand::ReleaseDevice tears the
stream down immediately (cancelling the deferred drop), freeing the hw:
grab + its reservation, then un-suspends the parked sink and resets any
forced graph clock (both self-gating). It does NOT reopen, unlike
reinit_device which would re-grab the device.

UI: a refresh-cw icon button beside the Output device select, propagated
through the settings callback chain to handle_release_device, which
releases, waits for PipeWire to reclaim, then re-enumerates so a freed or
hot-plugged DAC reappears without an app restart.

cc

crates/qbz-slint/ui/shell/AppShell.slint

@@ -54,6 +54,7 @@ export component AppShell inherits Rectangle {
     callback settings-select(string, int);
     callback settings-slider(string, int);
     callback settings-reset();
+    callback settings-release-device();
     callback logout();
     callback close-app();
 
@@ -255,6 +256,9 @@ export component AppShell inherits Rectangle {
                     settings-reset => {
                         root.settings-reset();
                     }
+                    settings-release-device => {
+                        root.settings-release-device();
+                    }
                 }
                 if NavState.view == ContentView.search: SearchResultsView {
                     open-album(id) => {