feat(conversations): remove unread count feature flag (CW-7237) (#14610)

## Description

Make conversation unread counts always available at runtime by removing
account feature checks from the API endpoint, unread-count listener,
notifier, and ActionCable broadcast path.

Update the dashboard to fetch sidebar unread counts for the active
account without checking FEATURE_FLAGS.CONVERSATION_UNREAD_COUNTS, and
remove the now-unused store clear action that only supported the
disabled state.

Keep the feature entry in config/features.yml to preserve flag bit
order, but mark it enabled and deprecated so fresh installs default to
the always-on behavior while feature-management UI hides it.

Leave existing installation default rows untouched; no migration is
included, so upgraded installs may still store the old flag value but
runtime behavior no longer depends on it.

Update specs around the new always-on contract and remove obsolete
disabled-feature assertions.

Fixes # CW-7237

## Type of change

Please delete options that are not relevant.

- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality not to work as expected)
- [ ] This change requires a documentation update

## How Has This Been Tested?

Update specs around the new always-on contract and remove obsolete
disabled-feature assertions. Ran specs locally for the changes.


## Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [ ] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

app/javascript/dashboard/helper/actionCable.js

@@ -13,7 +13,6 @@ import {
 } from 'dashboard/composables/useWhatsappCallSession';
 import { VOICE_CALL_PROVIDERS } from 'dashboard/helper/inbox';
 import { VOICE_CALL_DIRECTION } from 'dashboard/components-next/message/constants';
-import { FEATURE_FLAGS } from 'dashboard/featureFlags';
 
 const { isImpersonating } = useImpersonation();
 const UNREAD_COUNTS_REFETCH_THROTTLE_MS = 5000;
@@ -172,23 +171,10 @@ class ActionCableConnector extends BaseActionCableConnector {
   };
 
   fetchConversationUnreadCounts = () => {
-    if (!this.isConversationUnreadCountsEnabled()) return;
-
     this.lastUnreadCountsFetchAt = Date.now();
     this.app.$store.dispatch('conversationUnreadCounts/get');
   };
 
-  isConversationUnreadCountsEnabled = () => {
-    const accountId = this.app.$store.getters.getCurrentAccountId;
-    const isFeatureEnabled =
-      this.app.$store.getters['accounts/isFeatureEnabledonAccount'];
-
-    return isFeatureEnabled?.(
-      accountId,
-      FEATURE_FLAGS.CONVERSATION_UNREAD_COUNTS
-    );
-  };
-
   onTypingOn = ({ conversation, user }) => {
     const conversationId = conversation.id;