feat(push): M7 Part 2 — opt-in push notifications (embedded ntfy distributor)

Implements the app side of M7 push (docs/android/PLAN.md §11). The app EMBEDS
its own distributor — ntfy is only the relay server, no second app installed,
no Google Play Services. New feature slice; no existing screen's data flow
changes.

- core/push: NtfyTopic (random unguessable topic + endpoint/SSE URL builders),
  PushTickle (content-free { stream, ref } parser over ntfy's SSE envelope),
  NtfyStreamClient (bare-client OkHttp SSE to <ntfy>/<topic>/sse, reconnect/
  backoff cloned from ShardStreamClient), PushNotifier (channels + per-stream
  deep-link notification), PushService (foreground service holding the
  connection), PushManager (mint topic / register-unregister device / start-stop,
  keyed to the session), PushPreferences (DataStore state).
- data: NotificationsApi + DTOs + NotificationsRepository over the merged
  /auth/me/devices + /auth/me/notifications/* contract; push block on SettingsDto.
- ui/notifications: settings screen + VM — per-stream toggles, personal streams
  greyed until a game account is linked, POST_NOTIFICATIONS request on enable.
- Navigation: Routes.NOTIFICATIONS + stream→route deep-link map, menu entry,
  RunicApp + MainActivity intent handling; teardown wired into logout + server
  switch (deregister while bearer valid) and every sign-out (local, via session
  observer).
- Manifest: POST_NOTIFICATIONS + FOREGROUND_SERVICE(_DATA_SYNC) + the service.

Deviation (recorded in PLAN.md): direct-ntfy transport, no UnifiedPush library
— the plan's stated likely path; keeps the APK Google-free and dependency-light,
with a PushResult/transport seam for a future FCM Play flavor. Requires the small
companion push.ntfyUrl settings field (website#<pr>).

18 new JVM tests; :app:testDebugUnitTest + lintDebug + assembleDebug green.

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

app/src/main/AndroidManifest.xml

@@ -6,6 +6,13 @@
     <uses-permission android:name="android.permission.INTERNET" />
     <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
 
+    <!-- Opt-in push notifications (M7): the runtime notification permission (API 33+)
+         and a foreground service that holds the persistent ntfy connection open — the
+         embedded UnifiedPush distributor, so no separate app is needed (PLAN.md §11). -->
+    <uses-permission android:name="android.permission.POST_NOTIFICATIONS" />
+    <uses-permission android:name="android.permission.FOREGROUND_SERVICE" />
+    <uses-permission android:name="android.permission.FOREGROUND_SERVICE_DATA_SYNC" />
+
     <application
         android:name=".RunicGatewayApp"
         android:allowBackup="true"
@@ -26,6 +33,13 @@
                 <category android:name="android.intent.category.LAUNCHER" />
             </intent-filter>
         </activity>
+
+        <!-- The embedded distributor's persistent ntfy connection (M7, PLAN.md §11).
+             dataSync foreground type; not exported — started only by PushManager. -->
+        <service
+            android:name=".core.push.PushService"
+            android:exported="false"
+            android:foregroundServiceType="dataSync" />
     </application>
 
 </manifest>