Added shared update notices

- Iris joins shared Volmit update checks and reports
- The iris.update permission controls update visibility
- general.updateNotifications defaults to enabled
- Accepted settings changes reconfigure update checks
- Shutdown removes the settings listener and closes update checks
- Tests cover persisted opt-outs and notifier lifecycle

adapters/bukkit/plugin/src/main/resources/plugin.yml

@@ -23,6 +23,9 @@ commands:
   iris:
     aliases: [ ir, irs ]
 permissions:
+  iris.update:
+    description: Allows viewing Iris updates in VolmLib's combined update reports.
+    default: op
   iris.debugdump:
     description: Allows creating and optionally uploading diagnostic reports.
     default: op