feat(pc-client): 通讯录入口整改 + 添加同事弹窗 + 发送错误提示（视觉规范 v1，B-52 施工 3/3）

- ContactSider：三个功能入口改为 20px 线性图标 + 36x36 浅蓝图标块 + 文字
  （①新的同事②添加同事③我的群聊），行高 44，删掉 48px PNG 大图
- 新增 AddColleague 弹窗：工号 + 可编辑验证消息 + 五态（默认/校验失败/发送中/成功/失败）
- 会话栏搜索框右侧新增「+」入口，两处打开同一个弹窗
- useSendMessage：空接收方明确提示、SDK 错误码映射中文提示
- 申请状态文案对齐规范：等待对方通过/已添加/已拒绝
- global.scss 补 --search-bg / --chat-bg token

Co-authored-by: multica-agent <github@multica.ai>

pc-client/src/i18n/resources/en.json

@@ -220,6 +220,7 @@
     "latestChat": "Recent Chats",
     "myFriend": "My Friends",
     "myGroup": "My Groups",
+    "addColleague": "Add Colleague",
     "groupName": "Group Name",
     "groupAvatar": "Group Avatar",
     "groupMember": "Group Members",
@@ -461,9 +462,9 @@
     "custom": "Custom"
   },
   "application": {
-    "agree": "Agree",
+    "agree": "Accept",
     "refuse": "Refuse",
-    "agreed": "Agreed",
+    "agreed": "Added",
     "refused": "Refused",
     "information": "Verification Information",
     "pending": "Pending Verification",