feat: initial qobuz-qt source

Lightweight Qt6 desktop client for Qobuz with a Rust audio backend
(Symphonia/CPAL via staticlib FFI). Mirrors the spotify-qt layout:
toolbar with playback controls, library/context docks on the left,
tabbed search side panel on the right, queue panel, now-playing dock.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

res/icons/go-down.svg

@@ -0,0 +1,14 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 22 22">
+  <defs id="defs3051">
+    <style type="text/css" id="current-color-scheme">
+      .ColorScheme-Text {
+        color:#eff0f1;
+      }
+      </style>
+  </defs>
+ <path 
+    style="fill:currentColor;fill-opacity:1;stroke:none" 
+	d="m3.707031 7l-.707031.707031 6.125 6.125 1.875 1.875 1.875-1.875 6.125-6.125-.707031-.707031-6.125 6.125-1.167969 1.167969-1.167969-1.167969-6.125-6.125"
+    class="ColorScheme-Text"
+    />  
+</svg>