chore: Enable Participating tab for conversations (#11714)

## Summary

This PR enables the **Participating** conversation view in the main
sidebar and keeps the behavior aligned with existing conversation views.

## What changed

- Added **Participating** under Conversations in the new sidebar.
- Added a guard in conversation realtime `addConversation` flow so
generic `conversation.created` events are not injected while the user is
on Participating view.
- Added participating route mapping in conversation-list redirect helper
so list redirects resolve correctly to `/participating/conversations`.

## Scope notes

- Kept changes minimal and consistent with current `develop` behavior.
- No additional update-event filtering was added beyond what existing
views already do.

---------


Co-authored-by: Sivin Varghese <64252451+iamsivin@users.noreply.github.com>
Co-authored-by: iamsivin <iamsivin@gmail.com>

app/javascript/dashboard/helper/specs/URLHelper.spec.js

@@ -40,6 +40,15 @@ describe('#URL Helpers', () => {
         '/app/accounts/1/custom_view/1'
       );
     });
+
+    it('should return url to participating conversations', () => {
+      expect(
+        conversationListPageURL({
+          accountId: 1,
+          conversationType: 'participating',
+        })
+      ).toBe('/app/accounts/1/participating/conversations');
+    });
   });
   describe('conversationUrl', () => {
     it('should return direct conversation URL if activeInbox is nil', () => {