feat: Agent assignment policy index page with CRUD actions (#12373)

# Pull Request Template

## Description

This PR incudes new Agent assignment policy index page with CRUD
actions.

Fixes
https://linear.app/chatwoot/issue/CW-5570/feat-assignment-policy-index-page-with-actions

## Type of change

- [x] New feature (non-breaking change which adds functionality)

## How Has This Been Tested?

### Loom

https://www.loom.com/share/17ab5ceca4854f179628a3b53f347e5a?sid=cb64e881-57fd-4ae1-921b-7648653cca33

### Screenshots

**Light mode**
<img width="1428" height="888" alt="image"
src="https://github.com/user-attachments/assets/fdbb83e9-1f4f-4432-9e8a-4a8f1b810d31"
/>


**Dark mode**
<img width="1428" height="888" alt="image"
src="https://github.com/user-attachments/assets/f1fb38b9-1150-482c-ba62-3fe63ee1c7d4"
/>
<img width="726" height="495" alt="image"
src="https://github.com/user-attachments/assets/90a6ad55-9ab6-4adb-93a7-2327f5f09c79"
/>


## 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
- [ ] 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

---------

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

app/javascript/dashboard/api/specs/assignmentPolicies.spec.js

@@ -0,0 +1,70 @@
+import assignmentPolicies from '../assignmentPolicies';
+import ApiClient from '../ApiClient';
+
+describe('#AssignmentPoliciesAPI', () => {
+  it('creates correct instance', () => {
+    expect(assignmentPolicies).toBeInstanceOf(ApiClient);
+    expect(assignmentPolicies).toHaveProperty('get');
+    expect(assignmentPolicies).toHaveProperty('show');
+    expect(assignmentPolicies).toHaveProperty('create');
+    expect(assignmentPolicies).toHaveProperty('update');
+    expect(assignmentPolicies).toHaveProperty('delete');
+    expect(assignmentPolicies).toHaveProperty('getInboxes');
+    expect(assignmentPolicies).toHaveProperty('setInboxPolicy');
+    expect(assignmentPolicies).toHaveProperty('getInboxPolicy');
+    expect(assignmentPolicies).toHaveProperty('removeInboxPolicy');
+  });
+
+  describe('API calls', () => {
+    const originalAxios = window.axios;
+    const axiosMock = {
+      get: vi.fn(() => Promise.resolve()),
+      post: vi.fn(() => Promise.resolve()),
+      delete: vi.fn(() => Promise.resolve()),
+    };
+
+    beforeEach(() => {
+      window.axios = axiosMock;
+      // Mock accountIdFromRoute
+      Object.defineProperty(assignmentPolicies, 'accountIdFromRoute', {
+        get: () => '1',
+        configurable: true,
+      });
+    });
+
+    afterEach(() => {
+      window.axios = originalAxios;
+    });
+
+    it('#getInboxes', () => {
+      assignmentPolicies.getInboxes(123);
+      expect(axiosMock.get).toHaveBeenCalledWith(
+        '/api/v1/accounts/1/assignment_policies/123/inboxes'
+      );
+    });
+
+    it('#setInboxPolicy', () => {
+      assignmentPolicies.setInboxPolicy(456, 123);
+      expect(axiosMock.post).toHaveBeenCalledWith(
+        '/api/v1/accounts/1/inboxes/456/assignment_policy',
+        {
+          assignment_policy_id: 123,
+        }
+      );
+    });
+
+    it('#getInboxPolicy', () => {
+      assignmentPolicies.getInboxPolicy(456);
+      expect(axiosMock.get).toHaveBeenCalledWith(
+        '/api/v1/accounts/1/inboxes/456/assignment_policy'
+      );
+    });
+
+    it('#removeInboxPolicy', () => {
+      assignmentPolicies.removeInboxPolicy(456);
+      expect(axiosMock.delete).toHaveBeenCalledWith(
+        '/api/v1/accounts/1/inboxes/456/assignment_policy'
+      );
+    });
+  });
+});