新增 pc-client：畅联 PC 端工程（Electron+React，按确认效果图改造，B-59）

- 基于 openim-electron-demo 改造：工号+密码登录（自研账号服务）、会话列表/聊天窗/通讯录界面重做
- 文字/语音/文件/图片消息、文件拖拽发送、表情面板、一对一语音通话（LiveKit）
- RTC 令牌对接账号服务带鉴权版 /api/rtc_token（Bearer imToken + {room,identity}）
- account-service: CORS Allow-Headers 补 authorization（浏览器/渲染进程跨域调 rtc_token 需要）
- 附本地 mock 账号服务（scripts/mock-account-server.js）与截图联调脚本

pc-client/tailwind.config.js

@@ -0,0 +1,30 @@
+/** @type {import('tailwindcss').Config} */
+module.exports = {
+  content: ["./index.html", "./src/**/*.{js,ts,jsx,tsx}"],
+  theme: {
+    extend: {
+      padding: {
+        1.5: "0.375rem",
+        2.5: "0.625rem",
+        3.5: "0.875rem",
+        4.5: "1.125rem",
+        5.5: "1.375rem",
+        6.5: "1.625rem",
+      },
+      margin: {
+        2.5: "0.625rem",
+        3.5: "0.875rem",
+        4.5: "1.125rem",
+        5.5: "1.375rem",
+        6.5: "1.625rem",
+      },
+      width: {
+        10.5: "2.625rem",
+      },
+      height: {
+        10.5: "2.625rem",
+      },
+    },
+  },
+  darkMode: "class",
+};