fix(notifications): set dual-schedule fallbackBehavior to skip

Avoid showing default New Activity copy when dual content is missing or
outside contentTimeout, per PLUGIN_NOTIFICATION_FIX_ANDROID.md.

src/services/notifications/dualScheduleConfig.ts

@@ -78,7 +78,7 @@ export function buildDualScheduleConfig(
     relationship: {
       autoLink: true,
       contentTimeout: 5 * 60 * 1000, // 5 minutes
-      fallbackBehavior: "show_default",
+      fallbackBehavior: "skip", // was "show_default"
     },
   };
 }