android: the downloads say so in the shade

A Save still running with the app in the background now posts a progress
notice — how many files, the one it is on, a bar, Stop all and Open — and
takes it down when the queue empties. It sits on its own low-importance
channel so it can be silenced without silencing the player's card, and
rides its own dataSync foreground service rather than the media one: a
mediaPlayback service stops itself when the bar empties, a download is not
playback, and nothing else was keeping the process alive for a Save with
nothing playing — which is how the first real Save died, four tracks in.
Stop all goes through the same cancel(id) a row's tap takes, and Transfers
grew the matching button beside Clear finished. The walk pushes two rows
straight into the transfer store and reads the real notification back out
of `dumpsys notification`, without fetching anything.

crates/tauri-plugin-transfer-notice/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "tauri-plugin-transfer-notice"
+version = "0.1.0"
+description = "SoulStream's downloads in the phone's shade: a progress notification on its own low-importance channel, carried by its own dataSync foreground service, so a Save outlives the app going to the background"
+edition = "2021"
+rust-version = "1.77.2"
+# required by tauri-plugin's build script; must equal the crate name
+links = "tauri-plugin-transfer-notice"
+
+[dependencies]
+tauri = { version = "2", features = [] }
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+
+[build-dependencies]
+tauri-plugin = { version = "2", features = ["build"] }