Initial implementation of qobuz-qt

- Rust backend (qobuz-backend static lib): Qobuz API client (reqwest/tokio),
  Symphonia audio decoder, CPAL audio output, extern "C" FFI bridge
- Qt 6 frontend mirroring spotify-qt layout: toolbar with playback controls,
  left library dock, central track list, right search panel
- Auth: email/password login with MD5-signed requests; session token persisted
  via QSettings
- Playback: double-click a track → Rust fetches stream URL → Symphonia decodes
  → CPAL outputs to default audio device
- Dark Fusion palette matching spotify-qt feel

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

res.qrc

@@ -0,0 +1,6 @@
+<RCC>
+    <qresource prefix="/">
+        <!-- Icons will be served from the system theme; this is a fallback stub. -->
+        <!-- Add .svg files to res/icons/ and list them here if needed. -->
+    </qresource>
+</RCC>