feat: Enhance validation viewing functionality with event emission

- Updated the `createMarkViewedHandler` to emit an event when a validation is marked as viewed, allowing the UI to update the unviewed count dynamically.
- Modified the `useUnviewedValidations` hook to handle the new event type for decrementing the unviewed validations count.
- Introduced a new event type `issue_validation_viewed` in the issue validation event type definition for better event handling.

apps/server/src/routes/github/index.ts

@@ -45,7 +45,7 @@ export function createGitHubRoutes(events: EventEmitter): Router {
   router.post(
     '/validation-mark-viewed',
     validatePathParams('projectPath'),
-    createMarkViewedHandler()
+    createMarkViewedHandler(events)
   );
 
   return router;