chore: bump version to 1.2.0

Updated:
- src-tauri/Cargo.toml
- src-tauri/tauri.conf.json
- package.json + package-lock.json
- snapcraft.yaml (root + packaging/)
- flake.nix
- Cargo.lock
- metainfo.xml (new release entry)
- README: Snap MPRIS limitation note with forum link

cc

snapcraft.yaml

@@ -3,7 +3,7 @@
 
 name: qbz-player
 title: "QBZ — Native Qobuz Client for Linux"
-version: '1.1.20'
+version: '1.2.0'
 summary: Native Qobuz player for Linux with bit-perfect audio and DAC control
 description: |
   QBZ is a native Linux desktop client for Qobuz™, designed for high-fidelity playback.
@@ -86,7 +86,7 @@ parts:
   qbz:
     plugin: rust
     source: https://github.com/vicrodh/qbz.git
-    source-tag: v1.1.20
+    source-tag: v1.2.0
     build-packages:
       - libwebkit2gtk-4.1-dev
       - libgtk-3-dev