chore(release): bump version to 1.2.8 "My QBZ"

Mixtapes & Collections release. Bumps all version references
(Cargo.toml, tauri.conf.json, package.json, snapcraft.yaml, both
Cargo.lock, package-lock.json), adds the 1.2.8 entry to the Flatpak
metainfo, and sets the About modal codename to "My QBZ".

cc

snapcraft.yaml

@@ -3,7 +3,7 @@
 
 name: qbz-player
 title: "QBZ — Native Qobuz Client for Linux"
-version: '1.2.7'
+version: '1.2.8'
 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.