Notifications: Cleaned up mails, added debounce for updates

- Updated mail notification design to be a bit prettier, and extracted
  text to new lang file for translation.
- Added debounce logic for page update notifications.
- Fixed watch options not being filtered to current user.

app/Activity/Notifications/Handlers/NotificationHandler.php

@@ -2,6 +2,7 @@
 
 namespace BookStack\Activity\Notifications\Handlers;
 
+use BookStack\Activity\Models\Activity;
 use BookStack\Activity\Models\Loggable;
 use BookStack\Users\Models\User;
 
@@ -9,8 +10,8 @@ interface NotificationHandler
 {
     /**
      * Run this handler.
-     * Provides the activity type, related activity detail/model
+     * Provides the activity, related activity detail/model
      * along with the user that triggered the activity.
      */
-    public function handle(string $activityType, string|Loggable $detail, User $user): void;
+    public function handle(Activity $activity, string|Loggable $detail, User $user): void;
 }