feat(updater): add native update channels and one-line installation

Support Flatpak portal updates and signed Windows MSI upgrades. Add the Linux/macOS installer for 2.1.2, release signing, translations and regression coverage.

cx

crates/qbz-updater/Cargo.toml

@@ -18,3 +18,12 @@ rusqlite = { version = "0.40", features = ["bundled"] }
 tempfile = "3"
 flate2 = "1"
 tar = "0.4"
+
+[target.'cfg(target_os = "linux")'.dependencies]
+# Match Qt/ksni: never enable zbus/tokio through feature unification.
+zbus = { version = "5", default-features = false, features = ["async-io"] }
+futures-util = "0.3"
+
+[target.'cfg(windows)'.dependencies]
+sha2 = "0.10"
+windows-sys = { version = "0.61", features = ["Win32_System_Registry"] }