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

src-tauri/Cargo.lock

@@ -4910,7 +4910,7 @@ dependencies = [
 
 [[package]]
 name = "qbz-nix"
-version = "1.2.7"
+version = "1.2.8"
 dependencies = [
  "aes-gcm",
  "anyhow",