fix(i18n): correct zh/zh_CN conversation assignment message translations (#14033)

## Summary

The `assignee_name` and `user_name` variables are swapped in the Chinese
(zh/zh_CN) locale files for conversation assignment activity messages,
causing the rendered text to show the wrong person as the assignee.

### Before (incorrect)

| Template | English (correct) | Chinese (incorrect) |
|---|---|---|
| `assignee.assigned` | Assigned to **AgentA** by **Admin** | 由
**AgentA** 分配给 **Admin** |
| `team.assigned` | Assigned to **TeamX** by **Admin** | 由 **TeamX** 分配给
**Admin** |
| `team.assigned_with_assignee` | Assigned to **AgentA** via **TeamX**
by **Admin** | 由 **AgentA** 分配给 **TeamX** 团队的 **Admin** |

The Chinese text reads as if the conversation was assigned **to Admin**
(the API caller), when it was actually assigned **to AgentA**.

### After (correct)

| Template | Chinese (fixed) |
|---|---|
| `assignee.assigned` | 由 **Admin** 分配给 **AgentA** |
| `team.assigned` | 由 **Admin** 分配给 **TeamX** |
| `team.assigned_with_assignee` | 由 **Admin** 通过 **TeamX** 团队分配给
**AgentA** |

Now correctly matches the English template semantics.

## Files Changed

- `config/locales/zh_CN.yml` — 3 lines
- `config/locales/zh.yml` — 3 lines

## How to Verify

1. Set locale to `zh_CN`
2. Have an admin assign a conversation to an agent
3. Check the activity message in the conversation — the assignee name
should appear after "分配给", not before it

Co-authored-by: Sojan Jose <sojan@pepalo.com>

config/locales/zh.yml

@@ -244,11 +244,11 @@ zh:
         removed: '%{user_name} 取消了优先级'
       assignee:
         self_assigned: '%{user_name} 自行分配这次会话'
-        assigned: '由 %{assignee_name} 分配给 %{user_name}'
+        assigned: '由 %{user_name} 分配给 %{assignee_name}'
         removed: '对话未被 %{user_name} 分配'
       team:
-        assigned: '由 %{team_name} 分配给 %{user_name}'
-        assigned_with_assignee: '由 %{assignee_name} 分配给 %{team_name} 团队的 %{user_name}'
+        assigned: '由 %{user_name} 分配给 %{team_name}'
+        assigned_with_assignee: '由 %{user_name} 通过 %{team_name} 团队分配给 %{assignee_name}'
         removed: '由 %{user_name} 从 %{team_name} 中取消分配'
       labels:
         added: '%{user_name} 添加 %{labels}'

config/locales/zh_CN.yml

@@ -247,11 +247,11 @@ zh_CN:
         removed: '%{user_name} 取消了优先级'
       assignee:
         self_assigned: '%{user_name} 自行分配这次会话'
-        assigned: '由 %{assignee_name} 分配给 %{user_name}'
+        assigned: '由 %{user_name} 分配给 %{assignee_name}'
         removed: '对话未被 %{user_name} 分配'
       team:
-        assigned: '由 %{team_name} 分配给 %{user_name}'
-        assigned_with_assignee: '由 %{assignee_name} 分配给 %{team_name} 团队的 %{user_name}'
+        assigned: '由 %{user_name} 分配给 %{team_name}'
+        assigned_with_assignee: '由 %{user_name} 通过 %{team_name} 团队分配给 %{assignee_name}'
         removed: '由 %{user_name} 从 %{team_name} 中取消分配'
       labels:
         added: '%{user_name} 添加 %{labels}'