fix(subsonic): sync Rust HTTP UA with main webview UA (#235)

Use the main window WebView user agent as the runtime source for Rust-side HTTP clients and refresh the audio engine client when the UA changes. This keeps backend and WebView requests aligned while preserving a simple startup sync flow.

src/main.tsx

@@ -1,5 +1,6 @@
 import { StrictMode } from 'react';
 import ReactDOM from 'react-dom/client';
+import { invoke } from '@tauri-apps/api/core';
 import { getCurrentWindow } from '@tauri-apps/api/window';
 import App from './App';
 import './i18n';
@@ -15,6 +16,19 @@ try {
   (window as any).__PSY_WINDOW_LABEL__ = 'main';
 }
 
+// Sync backend HTTP User-Agent from the main webview once at startup.
+try {
+  const windowLabel = (window as any).__PSY_WINDOW_LABEL__ ?? 'main';
+  if (windowLabel === 'main') {
+    const ua = window.navigator.userAgent?.trim();
+    if (ua) {
+      void invoke('set_subsonic_wire_user_agent', { userAgent: ua, windowLabel });
+    }
+  }
+} catch {
+  // Ignore in non-Tauri runtimes.
+}
+
 ReactDOM.createRoot(document.getElementById('root')!).render(
   <StrictMode>
     <App />