fix: Translate "None" option in agent assignment dropdown (#11060)

# Pull Request Template

## Description

This PR includes a translation update for the "None" option in the agent
assignment multi-select dropdown.

Fixes
https://linear.app/chatwoot/issue/CW-4140/none-option-in-assign-agent-multi-select-is-not-translated

## Type of change

- [x] Bug fix (non-breaking change which fixes an issue)

## How Has This Been Tested?

**Test cases**
1. Check in conversation sidebar
2. Check in command bar
3. Check in participation dropdown


## Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [x] 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/composables/useAgentsList.js

@@ -1,9 +1,9 @@
 import { computed } from 'vue';
 import { useMapGetter } from 'dashboard/composables/store';
+import { useI18n } from 'vue-i18n';
 import {
   getAgentsByUpdatedPresence,
   getSortedAgentsByAvailability,
-  getCombinedAgents,
 } from 'dashboard/helper/agentHelper';
 
 /**
@@ -13,6 +13,7 @@ import {
  * @returns {Object} An object containing the agents list and assignable agents.
  */
 export function useAgentsList(includeNoneAgent = true) {
+  const { t } = useI18n();
   const currentUser = useMapGetter('getCurrentUser');
   const currentChat = useMapGetter('getSelectedChat');
   const currentAccountId = useMapGetter('getCurrentAccountId');
@@ -21,6 +22,19 @@ export function useAgentsList(includeNoneAgent = true) {
   const inboxId = computed(() => currentChat.value?.inbox_id);
   const isAgentSelected = computed(() => currentChat.value?.meta?.assignee);
 
+  /**
+   * Creates a 'None' agent object
+   * @returns {Object} None agent object
+   */
+  const createNoneAgent = () => ({
+    confirmed: true,
+    name: t('AGENT_MGMT.MULTI_SELECTOR.LIST.NONE') || 'None',
+    id: 0,
+    role: 'agent',
+    account_id: 0,
+    email: 'None',
+  });
+
   /**
    * @type {import('vue').ComputedRef<Array>}
    */
@@ -43,11 +57,10 @@ export function useAgentsList(includeNoneAgent = true) {
       agentsByUpdatedPresence
     );
 
-    return getCombinedAgents(
-      filteredAgentsByAvailability,
-      includeNoneAgent,
-      isAgentSelected.value
-    );
+    return [
+      ...(includeNoneAgent && isAgentSelected.value ? [createNoneAgent()] : []),
+      ...filteredAgentsByAvailability,
+    ];
   });
 
   return {