feat(desktop-client): add settings window and switch default API to production

- Open a dedicated settings BrowserWindow with general / login / diagnostics / about tabs
- Persist openAtLogin and keepRunningInBackground via desktop-settings.json; hide main window instead of quitting when background mode is on
- Default API base URL now points to api.shengxintui.com; LoginView and SettingsView share a single constant
- Restore wangyihao session cookies on probe and silent refresh, and accept the legacy http://mp.163.com console origin
- Drop the standalone diagnostics view in favor of the settings tab

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/desktop-client/src/renderer/App.vue

@@ -4,9 +4,10 @@ import { useDesktopSession } from "./composables/useDesktopSession";
 
 const DesktopShell = defineAsyncComponent(() => import("./components/DesktopShell.vue"));
 const LoginView = defineAsyncComponent(() => import("./views/LoginView.vue"));
+const SettingsWindow = defineAsyncComponent(() => import("./views/SettingsWindow.vue"));
 
 const { isAuthenticated, syncRuntimeSession } = useDesktopSession();
-type RendererWindowMode = "auto" | "login" | "main";
+type RendererWindowMode = "auto" | "login" | "main" | "settings";
 
 interface WindowModeBridge {
   setWindowMode?: (
@@ -17,7 +18,7 @@ interface WindowModeBridge {
 
 function resolveRendererWindowMode(): RendererWindowMode {
   const mode = new URLSearchParams(window.location.search).get("window");
-  return mode === "login" || mode === "main" ? mode : "auto";
+  return mode === "login" || mode === "main" || mode === "settings" ? mode : "auto";
 }
 
 function getModeBridge(): WindowModeBridge | undefined {
@@ -31,7 +32,9 @@ function syncWindowMode(authenticated: boolean): void {
 }
 
 const rendererWindowMode = resolveRendererWindowMode();
+document.documentElement.dataset.windowMode = rendererWindowMode;
 const usesAutomaticWindowMode = rendererWindowMode === "auto";
+const showsSettingsSurface = rendererWindowMode === "settings";
 const showsMainSurface = computed(() =>
   rendererWindowMode === "main" || (rendererWindowMode === "auto" && isAuthenticated.value),
 );
@@ -63,6 +66,18 @@ onMounted(() => {
 </script>
 
 <template>
-  <DesktopShell v-if="showsMainSurface" />
+  <SettingsWindow v-if="showsSettingsSurface" />
+  <DesktopShell v-else-if="showsMainSurface" />
   <LoginView v-else />
 </template>
+
+<style>
+html,
+body,
+#app {
+  width: 100%;
+  height: 100%;
+  overflow: hidden;
+}
+
+</style>