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.

src-tauri/Cargo.toml

@@ -60,6 +60,10 @@ audio-formats = { path = "../crates/audio-formats" }
 tauri-plugin-media-session = { path = "../crates/tauri-plugin-media-session" }
 tauri-plugin-storage = { path = "../crates/tauri-plugin-storage" }
 tauri-plugin-share = { path = "../crates/tauri-plugin-share" }
+# The phone's downloads notice (a second Kotlin foreground service, dataSync).
+# Registered everywhere so the permission set resolves on every platform; on
+# the desktop its commands answer "not here".
+tauri-plugin-transfer-notice = { path = "../crates/tauri-plugin-transfer-notice" }
 semver = "1"
 tauri-plugin-opener = "2.5.5"