fix: guard agent sort against null names in assignment dropdown (#15125)

# Pull Request Template

## Description

This PR fixes a crash where opening a conversation threw `TypeError:
Cannot read properties of null (reading 'localeCompare')` and prevented
the agent assignment dropdown from rendering.

Since #14866, agent bots are included in the assignable agents list.
`AgentBot#name` is not presence-validated, so system bots (account-less,
global) can have a `null` name. Those nameless bots flowed into
name-based operations that assumed a string, causing crashes and
warnings across multiple surfaces:

* **Assignment dropdown sort:** `getAgentsByAvailability` called
`a.name.localeCompare(b.name)`, causing a `localeCompare` `TypeError`.
* **Dropdown search:** `MultiselectDropdownItems` called
`option.name.toLowerCase()`, causing a `toLowerCase` `TypeError`.
* **Agent Bots settings:** `Avatar` received `name=null` for a `String`
prop, triggering a Vue prop validation warning.

### What changed

* Keep nameless agent bots in the assignment dropdown and render a `-`
fallback label in `useAgentsList`. These are still valid,
assignable-by-ID records: the assignable agents API includes accessible
bots, and `Conversations::AssignmentService` assigns them by ID.
Preserving them avoids hiding valid assignment targets. Bots are still
included only when `includeAgentBots` is enabled.
* Make the sort in `getAgentsByAvailability` null-safe by coercing
missing names to an empty string (defense in depth).
* Make the search filter in `MultiselectDropdownItems` null-safe
(defense in depth).
* Pass a null-safe `name` prop to `Avatar` in the Agent Bots settings
list to eliminate the Vue prop validation warning.

Fixes
https://linear.app/chatwoot/issue/CW-7670/agent-assignment-dropdown-crashes-with-cannot-read-properties-of-null

## Type of change

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

## How Has This Been Tested?


1. Have a system agent bot (`name: null`) that is assignable to an
inbox.
2. Open any conversation in that inbox.
   * The agent assignment dropdown renders without console errors.
   * The nameless bot is listed with a `-` label and can be assigned.
3. Go to **Settings → Agent Bots**.
   * The page renders without the `Avatar` prop validation warning.


## 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/spec/useAgentsList.spec.js

@@ -1,9 +1,9 @@
-import { ref } from 'vue';
-import { describe, it, expect, vi, beforeEach } from 'vitest';
-import { useAgentsList } from '../useAgentsList';
 import { useMapGetter } from 'dashboard/composables/store';
-import { allAgentsData, formattedAgentsData } from './fixtures/agentFixtures';
 import * as agentHelper from 'dashboard/helper/agentHelper';
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+import { ref } from 'vue';
+import { useAgentsList } from '../useAgentsList';
+import { allAgentsData, formattedAgentsData } from './fixtures/agentFixtures';
 
 // Mock vue-i18n
 vi.mock('vue-i18n', () => ({
@@ -94,6 +94,32 @@ describe('useAgentsList', () => {
     expect(agentsList.value.length).toBe(formattedAgentsData.slice(1).length);
   });
 
+  it('keeps nameless agent bots and applies a fallback label', () => {
+    const namelessBot = {
+      id: 91,
+      name: null,
+      assignee_type: 'AgentBot',
+      availability_status: 'offline',
+    };
+    mockUseMapGetter({
+      'inboxAssignableAgents/getAssignableAgents': ref(() => [
+        ...allAgentsData,
+        namelessBot,
+      ]),
+    });
+
+    const { agentsList } = useAgentsList();
+    // access the computed to trigger evaluation
+    expect(agentsList.value).toBeDefined();
+
+    const passedAgents =
+      agentHelper.getAgentsByUpdatedPresence.mock.calls[0][0];
+    expect(passedAgents).toContainEqual({
+      ...namelessBot,
+      name: '-',
+    });
+  });
+
   it('handles empty assignable agents', () => {
     mockUseMapGetter({
       'inboxAssignableAgents/getAssignableAgents': ref(() => []),

app/javascript/dashboard/composables/useAgentsList.js

@@ -1,10 +1,10 @@
-import { computed } from 'vue';
 import { useMapGetter } from 'dashboard/composables/store';
-import { useI18n } from 'vue-i18n';
 import {
   getAgentsByUpdatedPresence,
   getSortedAgentsByAvailability,
 } from 'dashboard/helper/agentHelper';
+import { computed } from 'vue';
+import { useI18n } from 'vue-i18n';
 
 /**
  * A composable function that provides a list of agents for assignment.
@@ -53,7 +53,11 @@ export function useAgentsList(
    * @type {import('vue').ComputedRef<Array>}
    */
   const agentsList = computed(() => {
-    const agents = assignableAgents.value || [];
+    const agents = (assignableAgents.value || []).map(agent =>
+      !agent.name && agent.assignee_type === 'AgentBot'
+        ? { ...agent, name: '-' }
+        : agent
+    );
     const agentsByUpdatedPresence = getAgentsByUpdatedPresence(
       agents,
       currentUser.value,