feat: quality profile selection in desktop settings

Adds a Quality dropdown (Auto / Opus 24k / Opus 6k / Codec2 3.2k /
Codec2 1.2k) to both the connect screen and settings panel. The
selected profile is passed through to the engine which configures
the encoder and decoder accordingly.

The desktop engine recv path now auto-switches the decoder codec
when incoming packets use a different codec than expected, enabling
cross-codec interop between clients on different quality settings.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

desktop/src-tauri/src/main.rs

@@ -122,6 +122,7 @@ async fn connect(
     room: String,
     alias: String,
     os_aec: bool,
+    quality: String,
 ) -> Result<String, String> {
     let mut engine_lock = state.engine.lock().await;
     if engine_lock.is_some() {
@@ -129,7 +130,7 @@ async fn connect(
     }
 
     let app_clone = app.clone();
-    match CallEngine::start(relay, room, alias, os_aec, move |event_kind, message| {
+    match CallEngine::start(relay, room, alias, os_aec, quality, move |event_kind, message| {
         let _ = app_clone.emit(
             "call-event",
             CallEvent {