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/components-next/sidebar/Sidebar.vue

@@ -250,6 +250,12 @@ const menuItems = computed(() => {
           activeOn: ['conversation_through_mentions'],
           to: accountScopedRoute('conversation_mentions'),
         },
+        {
+          name: 'Participating',
+          label: t('SIDEBAR.PARTICIPATING_CONVERSATIONS'),
+          activeOn: ['conversation_through_participating'],
+          to: accountScopedRoute('conversation_participating'),
+        },
         {
           name: 'Unattended',
           activeOn: ['conversation_through_unattended'],