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/permissions/default.toml

@@ -0,0 +1,9 @@
+"$schema" = "schemas/schema.json"
+
+[default]
+description = """
+The downloads notice on the phone: `update` mirrors what Save is fetching,
+`clear` takes it down, and the two listener commands are what lets the page
+hear the notice's buttons (`addPluginListener`).
+"""
+permissions = ["allow-update", "allow-clear", "allow-registerListener", "allow-removeListener"]