added telemetry call on app resume with 15 minute cooldown

lib/api/marianumconnect/queries/telemetry_heartbeat/telemetry_heartbeat.dart

@@ -12,8 +12,9 @@ import 'telemetry_device_id.dart';
 
 /// Sends a telemetry heartbeat to MarianumConnect (`POST me/telemetry`) —
 /// upserts the stable install id, platform, app version and device info. Sent
-/// once on app start and again once push registration completes that session
-/// (so a fresh registration isn't under-reported until the next launch).
+/// on app start, again once push registration completes that session (so a
+/// fresh registration isn't under-reported until the next launch), and on
+/// resume after the app spent more than 15 minutes in the background.
 /// Bearer-authenticated via the shared dio interceptor. Replaces the legacy
 /// mhsl.eu `server/userIndex/update` call.
 class TelemetryHeartbeat extends MarianumConnectQuery {
@@ -21,7 +22,8 @@ class TelemetryHeartbeat extends MarianumConnectQuery {
 
   /// Fire-and-forget: schedules a heartbeat and swallows any error, so a failed
   /// send never disrupts app start. Used from the app shell's initState and
-  /// re-emitted once push registration completes (see `_MainState._syncPush`).
+  /// lifecycle handler, and re-emitted once push registration completes (see
+  /// `_MainState._syncPush`).
   static void report({required bool notificationsEnabled}) {
     unawaited(
       TelemetryHeartbeat()