feature: Phase 18.6 Track A — public Settings menu + streaming-quality toggle

DeepDrftPublic.Client/Common/StreamQuality.cs

@@ -0,0 +1,18 @@
+namespace DeepDrftPublic.Client.Common;
+
+/// <summary>
+/// The listener's streaming-quality preference (Phase 18 wave 18.6, §4). This is the user's <em>intent</em>,
+/// not the wire format that ultimately gets served: <see cref="LowData"/> means "give me Opus if you can,"
+/// but the player still capability-gates and C2-falls-back to lossless when Opus can't play (a browser that
+/// can't decode Ogg Opus, or a track with no Opus artifact). It is therefore deliberately distinct from
+/// <c>DeepDrftModels.Enums.AudioFormat</c> (the delivery rendering resolved per request): one is the
+/// remembered preference, the other is what a given stream request actually asks for.
+/// </summary>
+public enum StreamQuality
+{
+    /// <summary>Bandwidth-friendly Opus (capability-gated; the default before any choice — OQ2).</summary>
+    LowData,
+
+    /// <summary>The lossless WAV path, always playable everywhere.</summary>
+    Lossless
+}