Add persistent notifications for priority 10 messages

- Implement custom PersistentNotification widget with flashing background
- Add settings for persistent priority 10 notifications and sound control
- Modify notification logic to show persistent pop-ups for priority 10
- Allow closing all persistent notifications via tray icon click
- Add AGENTS.md with type checking guidelines
- Configure pyright to suppress PyQt6 false positives
- Update UI in settings dialog for new options
- Add notification sound file

pyrightconfig.json

@@ -0,0 +1,8 @@
+{
+  "reportOptionalMemberAccess": false,
+  "reportAttributeAccessIssue": false,
+  "reportIncompatibleMethodOverride": false,
+  "reportArgumentType": false,
+  "reportAssignmentType": false,
+  "reportReturnType": false
+}