chore(release): bump version to 1.2.9 + tag notes

Quiet Polish: QConnect cleanup (#316) and a long round of Linux
tray polish. Sticky-header gap fix (no more padding-top on scroll
containers), Edit folder shortcut from the playlist sidebar (#364),
shift-range + Ctrl/Cmd+A multi-select across the remaining views,
opt-in resume of seek position (#317), and Qobuz subtitle/edition
propagated through queue / MPRIS / scrobbling (#360).

Bumped:
- src-tauri/Cargo.toml + Cargo.lock
- src-tauri/tauri.conf.json
- package.json + package-lock.json
- snapcraft.yaml (version + source-tag)
- packaging/flatpak/com.blitzfc.qbz.metainfo.xml (new release entry)

packaging/snap/snapcraft.yaml is a symlink to the root snapcraft.yaml
so it tracks automatically.

cc

src-tauri/Cargo.lock

@@ -4911,7 +4911,7 @@ dependencies = [
 
 [[package]]
 name = "qbz-nix"
-version = "1.2.8"
+version = "1.2.9"
 dependencies = [
  "aes-gcm",
  "anyhow",