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/helper/specs/agentHelper.spec.js

@@ -2,8 +2,6 @@ import {
   getAgentsByAvailability,
   getSortedAgentsByAvailability,
   getAgentsByUpdatedPresence,
-  getCombinedAgents,
-  createNoneAgent,
 } from '../agentHelper';
 import {
   allAgentsData,
@@ -93,39 +91,4 @@ describe('agentHelper', () => {
       ).toEqual([]);
     });
   });
-
-  describe('getCombinedAgents', () => {
-    it('includes None agent when includeNoneAgent is true and isAgentSelected is true', () => {
-      const result = getCombinedAgents(sortedByAvailability, true, true);
-      expect(result).toEqual([createNoneAgent, ...sortedByAvailability]);
-      expect(result.length).toBe(sortedByAvailability.length + 1);
-      expect(result[0]).toEqual(createNoneAgent);
-    });
-
-    it('excludes None agent when includeNoneAgent is false', () => {
-      const result = getCombinedAgents(sortedByAvailability, false, true);
-      expect(result).toEqual(sortedByAvailability);
-      expect(result.length).toBe(sortedByAvailability.length);
-      expect(result[0]).not.toEqual(createNoneAgent);
-    });
-
-    it('excludes None agent when isAgentSelected is false', () => {
-      const result = getCombinedAgents(sortedByAvailability, true, false);
-      expect(result).toEqual(sortedByAvailability);
-      expect(result.length).toBe(sortedByAvailability.length);
-      expect(result[0]).not.toEqual(createNoneAgent);
-    });
-
-    it('returns only filtered agents when both includeNoneAgent and isAgentSelected are false', () => {
-      const result = getCombinedAgents(sortedByAvailability, false, false);
-      expect(result).toEqual(sortedByAvailability);
-      expect(result.length).toBe(sortedByAvailability.length);
-    });
-
-    it('handles empty filteredAgentsByAvailability array', () => {
-      const result = getCombinedAgents([], true, true);
-      expect(result).toEqual([createNoneAgent]);
-      expect(result.length).toBe(1);
-    });
-  });
 });