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/android/src/main/AndroidManifest.xml

@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+    <!-- the foreground service that carries the downloads while the app is
+         in the background; a fetch is dataSync, not playback -->
+    <uses-permission android:name="android.permission.FOREGROUND_SERVICE" />
+    <uses-permission android:name="android.permission.FOREGROUND_SERVICE_DATA_SYNC" />
+    <!-- the notice is a notification; asked for at runtime on Android 13+ -->
+    <uses-permission android:name="android.permission.POST_NOTIFICATIONS" />
+
+    <application>
+        <!-- no intent filter: the notice's own buttons come back as
+             onStartCommand intents on this very service -->
+        <service
+            android:name="com.soulstream.transfernotice.TransferService"
+            android:exported="false"
+            android:foregroundServiceType="dataSync" />
+    </application>
+</manifest>