feat(android): notifications when the app is closed, a specialUse delivery service (#5347)

Roundtable's shape: no FCM. A specialUse foreground service keeps the
process alive; EventsStream stays connected; DeliveryLauncher runs the
catch-up on every notification.created nudge and every reconnect, and is
the single owner of the service's lifetime (signed in AND the device's
"Notifications when the app is closed", on by default).

- NotificationSync pulls the newest page and announces unread notices past
  a high-water mark (auth_session.notifiedUpTo, read and written through
  the DAO), honouring the per-kind phone pref. A first look sets the mark
  without announcing; more than three collapse to one line; nothing is
  posted while the app is on screen.
- Two channels: "Your requests" and "Library health"; the ongoing notice
  sits on a MIN "Background connection" channel.
- EventsStream: a connected flow, 2s→5min backoff with ±25% jitter, and an
  immediate reconnect when a network comes up (a hint, not VALIDATED) or
  the app comes to the foreground.
- BootReceiver restarts delivery after a reboot or a self-update.
- A tap opens what the notice links to (routeForLink), a pile the inbox.
- POST_NOTIFICATIONS is asked for on Android 13+ once delivery is wanted,
  and again when the toggle is turned on.
- Room v12: auth_session.backgroundDelivery and notifiedUpTo.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

android/app/src/main/res/drawable/ic_notification.xml

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Status-bar icon for Minstrel's own notifications (M489 #5347): Lucide's
+     bell, stroked in white. The system tints it; only the alpha is used. -->
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24">
+    <path
+        android:pathData="M6,8a6,6 0,0 1,12 0c0,7 3,9 3,9H3s3,-2 3,-9"
+        android:strokeColor="#FFFFFFFF"
+        android:strokeWidth="2"
+        android:strokeLineCap="round"
+        android:strokeLineJoin="round" />
+    <path
+        android:pathData="M10.3,21a1.94,1.94 0,0 0,3.4 0"
+        android:strokeColor="#FFFFFFFF"
+        android:strokeWidth="2"
+        android:strokeLineCap="round"
+        android:strokeLineJoin="round" />
+</vector>