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/src/pages/login/index.tsx

@@ -0,0 +1,55 @@
+import { t } from "i18next";
+import { useCopyToClipboard } from "react-use";
+
+import login_bg from "@/assets/images/login/login_bg.png";
+import WindowControlBar from "@/components/WindowControlBar";
+import { APP_NAME, APP_VERSION, SDK_VERSION } from "@/config";
+import { feedbackToast } from "@/utils/common";
+
+import styles from "./index.module.scss";
+import LoginForm from "./LoginForm";
+
+export const Login = () => {
+  const [_, copyToClipboard] = useCopyToClipboard();
+
+  const handleCopy = () => {
+    copyToClipboard(`${`${APP_NAME} ${APP_VERSION}`}/${SDK_VERSION}`);
+    feedbackToast({ msg: t("toast.copySuccess") });
+  };
+
+  return (
+    <div className="relative flex h-full flex-col">
+      <div className="app-drag relative h-10 bg-[var(--top-search-bar)]">
+        <WindowControlBar />
+      </div>
+      <div className="flex flex-1 items-center justify-center">
+        <LeftBar />
+        <div
+          className={`${styles.login} mr-14 h-[450px] w-[350px] rounded-md bg-white p-11`}
+          style={{ boxShadow: "0 0 30px rgba(0,0,0,.1)" }}
+        >
+          <LoginForm />
+        </div>
+      </div>
+      <div
+        className="absolute bottom-3 right-3 flex cursor-pointer flex-col items-center text-xs"
+        onClick={handleCopy}
+      >
+        <div className="text-[var(--sub-text)]">{`${APP_NAME} ${APP_VERSION}`}</div>
+        <div className="text-[var(--sub-text)]">{SDK_VERSION}</div>
+      </div>
+    </div>
+  );
+};
+
+const LeftBar = () => {
+  return (
+    <div className="flex min-h-[420]">
+      <div className="mr-14 text-center">
+        <div className="text-2xl">{t("placeholder.title")}</div>
+        <span className="text-sm  text-gray-400">{t("placeholder.subTitle")}</span>
+        <img src={login_bg} alt="login_bg" />
+      </div>
+    </div>
+  );
+};