fix(packaging): Arch installs com.blitzfc.qbz.desktop for the MPRIS app icon

GNOME resolves the MPRIS media-widget app icon via DesktopEntry -> the installed
<id>.desktop -> Icon=. Rename the Arch desktop file to com.blitzfc.qbz.desktop,
set Icon=com.blitzfc.qbz, and install the hicolor icon as com.blitzfc.qbz.png so
the basename matches the published DesktopEntry. Other channels (AUR/Gentoo/Snap
+ Tauri bundle/release workflow) documented in qbz-nix-docs (release-time,
build-test required). Flatpak was already correct.

cc

packaging/arch/PKGBUILD

@@ -41,7 +41,9 @@ build() {
 package() {
   cd "${srcdir}/qbz-${pkgver}"
   install -Dm755 src-tauri/target/release/qbz "${pkgdir}/usr/bin/qbz"
-  install -Dm644 packaging/arch/qbz.desktop "${pkgdir}/usr/share/applications/qbz.desktop"
-  install -Dm644 src-tauri/icons/128x128.png "${pkgdir}/usr/share/icons/hicolor/128x128/apps/qbz.png"
+  # .desktop basename and Icon MUST be the app-id so GNOME resolves the MPRIS
+  # app icon (MPRIS DesktopEntry = com.blitzfc.qbz → <id>.desktop → Icon=).
+  install -Dm644 packaging/arch/com.blitzfc.qbz.desktop "${pkgdir}/usr/share/applications/com.blitzfc.qbz.desktop"
+  install -Dm644 src-tauri/icons/128x128.png "${pkgdir}/usr/share/icons/hicolor/128x128/apps/com.blitzfc.qbz.png"
   install -Dm644 LICENSE "${pkgdir}/usr/share/licenses/${pkgname}/LICENSE"
 }

packaging/arch/com.blitzfc.qbz.desktop

@@ -3,7 +3,7 @@ Name=QBZ
 Comment=Native Qobuz client with hi-res audio support
 Exec=qbz %u
 Type=Application
-Icon=qbz
+Icon=com.blitzfc.qbz
 Categories=AudioVideo;Audio;Music;Player;
 Terminal=false
 StartupWMClass=com.blitzfc.qbz