feat: add volume control and merge sound mode feature

- Add volume control screen with sliders for media, ringtone, and alarm
- Update device settings via PUT /devices with CSV (same as language)
- Extract DeviceCsvBuilder to legacy_shared (shared between language and volume)
- Create Riverpod provider for DeviceUpdateDatasource
- Extract VolumeThumbShape to separate widget file
- Merge sound mode feature (SET_SOUND_MODE command, pending backend whitelist)
- Fix sound screen overflow with SingleChildScrollView

apps/mobile_app/lib/navigation/app_router.dart

@@ -141,6 +141,11 @@ void configureAppRouter() {
                     name: 'apps_use',
                     pageBuilder: const AppsUseBuilder().buildPage,
                   ),
+                  GoRoute(
+                    path: 'volume_control',
+                    name: 'volume_control',
+                    pageBuilder: const VolumeControlBuilder().buildPage,
+                  ),
                 ],
               ),
             ],