fix(gui): 桌面版真正加载渠道插件 + 外链一律交给默认浏览器

## ① 桌面版此前**完全没有插件系统**（渠道页根本不存在）
GUI 内嵌内核的 config.yaml 由 main.js 生成，唯独漏了 `plugin_dir` ——
而内核刻意不给它默认值（运维显式开启）。后果：桌面版 `plugin_dir: ""`，
`/api/plugins` 返回空列表，channels 插件（多平台账号登录、凭据保管、自动
领取）在桌面端**完全不可见**。实测复现：同一份配置去掉 plugin_dir 就是
`plugins: []`，加上就有 billing/channels/quota/usage 四个。

修法：
- 新 profile 直接写 `plugin_dir: <profile>/plugins`；
- **老 profile 回填**（用户已有 config.yaml，不写就只有老用户永远没有插件）——
  新增 `ensurePluginDirConfigured()`，只在缺少该键时追加，其余内容不动；
- 插件树由内核 SeedBundled 播种（按文件补齐，用户改过的副本优先保留）。

## ② 升级后渠道修复**下发不到桌面用户**
内核播种规则是「文件缺失才写」，所以桌面用户升级 GUI 后 `channels.lua`
仍是旧版 —— 我们发的渠道修复对桌面用户静默失效。桌面版必须自己处理：
按 app 版本打戳（`.plugin-seed-version`），版本变化时删掉 4 个内置插件文件
让新内核重新播种，旧副本留 `.prev-<旧版本>` 可人工恢复；用户自建插件不碰。
逻辑抽到 `cmd/gui/plugin-sync.js`（无 Electron 依赖），配 6 条 node 单测。

## ③ 登录一律拉起默认浏览器（三条路径都覆盖）
桌面版的内容区是加载内核 WebUI 的 iframe，渠道登录链接是 `target=_blank`。
此前只处理了 `setWindowOpenHandler`，另两条路径仍会把 Electron 窗口带到
第三方页面。现在三条路径统一外抛：
1. `window.open` / target=_blank  → setWindowOpenHandler
2. 顶层同标签跳转               → will-navigate
3. iframe 内导航                → will-frame-navigate
**loopback 例外必须保留**：channels 的服务端浏览器（noVNC）就在
`127.0.0.1:<port>` 的 iframe 里，拦掉它会让 VNC 登录失效。

实测（打包后的 GUI + Xvfb + CDP 驱动真实窗口）：
  [gui] open in default browser: https://example.com/mr-windowopen-probe
  [gui] open in default browser: https://example.com/mr-navigate-probe
  [gui] open in default browser: https://example.com/mr-frame-probe
  [gui] open in default browser: https://xiaohuanxiong.com/login?code=…（真实商汤登录链接）
顶层 URL 保持在内核页面（跳转被拦下），loopback iframe 正常加载。

## ④ 顺手
- GUI 版本号 1.9.7 → 2.0.42（与内核同版本发版；package-lock 里还是 1.9.3，
  一并同步）；
- `make gui-test` 跑桌面壳单测。

验证：打包后的 GUI 启动即 `/api/plugins` 列出 channels（ui.page=channels），
插件目录播种 4 个内置插件；外链四类实测均走默认浏览器。

cmd/gui/main.js

@@ -18,6 +18,7 @@ const http = require("http");
 const os = require("os");
 const crypto = require("crypto");
 const { spawn, execFileSync } = require("child_process");
+const pluginSync = require("./plugin-sync");
 
 const LOG_FILE = path.join(app.getPath("userData"), "gui.log");
 function log(msg) {
@@ -40,6 +41,13 @@ console.error = function () {
 // Per-user profile dir: <userData>/profile
 const PROFILE_DIR = path.join(app.getPath("userData"), "profile");
 const CONFIG_FILE = path.join(PROFILE_DIR, "config.yaml");
+// Plugin tree for the embedded core. The core deliberately does NOT default
+// plugin_dir (an operator opts in), so the desktop build must set it — without
+// it the whole plugin system stays off and the channels plugin (multi-platform
+// account login + credential vault + auto check-in) is invisible in the WebUI.
+// Seeding is the core's job (SeedBundled fills MISSING files only), so a user's
+// edited copy always wins.
+const PLUGINS_DIR = path.join(PROFILE_DIR, "plugins");
 // Packaged: extraResource at process.resourcesPath/bin (outside asar, spawnable).
 // Dev:   cmd/gui/bin, populated by prepare-core.js.
 const CORE_EXE = path.join(
@@ -216,6 +224,9 @@ function writeDefaultEmbeddedConfig() {
     "listen: 127.0.0.1:" + (settings.port || DEFAULT_PORT),
     "default_model: AUTO",
     "adapter_dir: " + JSON.stringify(path.join(PROFILE_DIR, "adapters")),
+    // Plugin tree: channels/billing/quota/usage ship inside the core binary and
+    // are seeded into this dir on first start. Omitting it disables plugins.
+    "plugin_dir: " + JSON.stringify(PLUGINS_DIR),
     "runtime_file: " + JSON.stringify(path.join(PROFILE_DIR, "runtime.json")),
     "",
     // Admin key as a plain `keys` entry (no seed flag) so the web UI never
@@ -268,6 +279,9 @@ function startCore() {
   // ensure profile dir + config + local adapters exist
   fs.mkdirSync(PROFILE_DIR, { recursive: true });
   if (!fs.existsSync(CONFIG_FILE)) writeDefaultEmbeddedConfig();
+  pluginSync.ensurePluginDirConfigured(CONFIG_FILE, PLUGINS_DIR, log);
+  fs.mkdirSync(PLUGINS_DIR, { recursive: true });
+  pluginSync.syncBundledPluginsOnUpgrade(PROFILE_DIR, PLUGINS_DIR, app.getVersion(), log);
 
   coreProc = spawn(CORE_EXE, ["-config", CONFIG_FILE], {
     cwd: PROFILE_DIR,
@@ -622,10 +636,55 @@ function createWindow() {
     },
   });
   mainWindow.loadFile(path.join(__dirname, "renderer", "index.html"));
+  // External links ALWAYS go to the user's default browser, never an in-app
+  // window. Three paths have to be covered, and missing any one of them is why
+  // "click the login link and nothing happens / the app navigates away" shows up:
+  //   1. window.open / target=_blank            -> setWindowOpenHandler
+  //   2. top-level navigation (same-tab click)  -> will-navigate
+  //   3. navigation inside the WebUI <iframe>   -> will-frame-navigate
+  // The embedded core's own origin (and file:// for the shell) must keep
+  // working, otherwise the WebUI and plugin pages stop loading.
+  const isInternal = (url) =>
+    !url ||
+    url === "about:blank" ||
+    url.startsWith("file://") ||
+    url.startsWith(embeddedBaseUrl()) ||
+    url.startsWith("devtools://");
+  const openExternally = (url) => {
+    if (url && (url.startsWith("http://") || url.startsWith("https://"))) {
+      log("[gui] open in default browser: " + url);
+      shell.openExternal(url);
+    }
+  };
   mainWindow.webContents.setWindowOpenHandler(({ url }) => {
-    if (url && url.startsWith("http")) shell.openExternal(url);
+    if (!isInternal(url)) openExternally(url);
     return { action: "deny" };
   });
+  mainWindow.webContents.on("will-navigate", (e, url) => {
+    if (isInternal(url)) return;
+    e.preventDefault();
+    openExternally(url);
+  });
+  // iframe navigations (the WebUI content area and the plugin pages inside it).
+  // The channels plugin renders its server-side login browser (noVNC) in an
+  // iframe on a LOOPBACK port, so loopback MUST stay in-app — blocking it would
+  // break VNC login. Everything non-loopback is external: open the default
+  // browser instead of silently replacing the gateway UI with a third-party page.
+  const isLoopback = (url) => {
+    try {
+      const h = new URL(url).hostname;
+      return h === "127.0.0.1" || h === "localhost" || h === "[::1]";
+    } catch (e) {
+      return false;
+    }
+  };
+  if (mainWindow.webContents.on) {
+    mainWindow.webContents.on("will-frame-navigate", (e) => {
+      if (isInternal(e.url) || isLoopback(e.url)) return;
+      e.preventDefault();
+      openExternally(e.url);
+    });
+  }
   // Silent start: `--silent` CLI flag or settings.silentStart keeps the app
   // in the tray without showing the window (Clash-Verge style). First run
   // always shows the window so the user sees the dashboard.