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

spec/controllers/api/v1/accounts/conversations_controller_spec.rb

@@ -126,47 +126,32 @@ RSpec.describe 'Conversations API', type: :request do
         Conversations::UnreadCounts::Store.clear_account!(account.id)
       end
 
-      context 'when conversation unread counts feature is enabled' do
-        before do
-          account.enable_features!(:conversation_unread_counts)
-        end
+      it 'returns unread conversation counts scoped to the signed-in user' do
+        create_unread_conversation(account: account, inbox: visible_inbox, labels: [label.title])
+        create_unread_conversation(account: account, inbox: hidden_inbox, labels: [label.title])
 
-        it 'returns unread conversation counts scoped to the signed-in user' do
-          create_unread_conversation(account: account, inbox: visible_inbox, labels: [label.title])
-          create_unread_conversation(account: account, inbox: hidden_inbox, labels: [label.title])
-
-          get "/api/v1/accounts/#{account.id}/conversations/unread_counts",
-              headers: agent.create_new_auth_token,
-              as: :json
-
-          expect(response).to have_http_status(:success)
-          expect(response.parsed_body['payload']).to eq(
-            'inboxes' => { visible_inbox.id.to_s => 1 },
-            'labels' => { label.id.to_s => 1 },
-            'teams' => {}
-          )
-        end
-
-        it 'returns unread team conversation counts scoped to the signed-in user' do
-          create_unread_conversation(account: account, inbox: visible_inbox, team: team)
-          create_unread_conversation(account: account, inbox: hidden_inbox, team: team)
-
-          get "/api/v1/accounts/#{account.id}/conversations/unread_counts",
-              headers: agent.create_new_auth_token,
-              as: :json
-
-          expect(response).to have_http_status(:success)
-          expect(response.parsed_body['payload']['teams']).to eq(team.id.to_s => 1)
-        end
-      end
-
-      it 'returns forbidden when conversation unread counts feature is disabled' do
         get "/api/v1/accounts/#{account.id}/conversations/unread_counts",
             headers: agent.create_new_auth_token,
             as: :json
 
-        expect(response).to have_http_status(:forbidden)
-        expect(response.parsed_body['error']).to eq('Conversation unread counts feature not enabled for this account')
+        expect(response).to have_http_status(:success)
+        expect(response.parsed_body['payload']).to eq(
+          'inboxes' => { visible_inbox.id.to_s => 1 },
+          'labels' => { label.id.to_s => 1 },
+          'teams' => {}
+        )
+      end
+
+      it 'returns unread team conversation counts scoped to the signed-in user' do
+        create_unread_conversation(account: account, inbox: visible_inbox, team: team)
+        create_unread_conversation(account: account, inbox: hidden_inbox, team: team)
+
+        get "/api/v1/accounts/#{account.id}/conversations/unread_counts",
+            headers: agent.create_new_auth_token,
+            as: :json
+
+        expect(response).to have_http_status(:success)
+        expect(response.parsed_body['payload']['teams']).to eq(team.id.to_s => 1)
       end
     end
   end
@@ -848,7 +833,6 @@ RSpec.describe 'Conversations API', type: :request do
       end
 
       it 'refreshes unread count cache when conversation is marked read' do
-        account.enable_features!(:conversation_unread_counts)
         conversation.update!(agent_last_seen_at: 1.hour.ago)
         create(:message, account: account, inbox: conversation.inbox, conversation: conversation, message_type: :incoming, created_at: 5.minutes.ago)
         Conversations::UnreadCounts::Builder.new(account).build_base!
@@ -936,7 +920,6 @@ RSpec.describe 'Conversations API', type: :request do
       end
 
       it 'refreshes unread count cache when conversation is marked unread' do
-        account.enable_features!(:conversation_unread_counts)
         conversation.update!(agent_last_seen_at: 1.minute.from_now, assignee_last_seen_at: 1.minute.from_now)
         Conversations::UnreadCounts::Builder.new(account).build_base!