proxy: include priority field in push notification JSON payload

The HTTP Urgency header set on WebPush requests is not exposed to
UnifiedPush Android clients by the connector library. Include a
"priority" field ("high" or "normal") directly in the JSON body
so that clients can determine whether a push notification requires
immediate wake-up processing or can be deferred until the next
natural activity.

This complements the daemon-side priority assignment (Gerrit #34059)
and allows UnifiedPush (F-Droid) builds to benefit from the same
battery savings as FCM builds.

Change-Id: Id316ff89e64e59d1b224f5b4e14da6b36dc62c95
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/dht_proxy_server.cpp

@@ -1191,7 +1191,13 @@ DhtProxyServer::handlePushListen(const InfoHash& infoHash,
                        minPriority,
                        values.size());
 
-    sendPushNotification(pushToken, std::move(json), type, !expired and minPriority == 0, topic);
+    // Include priority in the JSON payload so that UnifiedPush clients
+    // (which don't have access to the HTTP Urgency header) can determine
+    // whether a push requires immediate processing or can be deferred.
+    bool highPriority = !expired and minPriority == 0;
+    json["priority"] = highPriority ? "high" : "normal";
+
+    sendPushNotification(pushToken, std::move(json), type, highPriority, topic);
 
     return true;
 }