Allow desktop app to connect to selfhosted servers (#4902)

# Description of Changes
Changes the desktop app to allow connections to self-hosted servers on
first startup. This was quite involved and hit loads of CORS issues all
through the stack, but I think it's working now. This also changes the
bundled backend to spawn on an OS-decided port rather than always
spawning on `8080`, which means that the user can have other things
running on port `8080` now and the app will still work fine. There were
quite a few places that needed to be updated to decouple the app from
explicitly using `8080` and I was originally going to split those
changes out into another PR (#4939), but I couldn't get it working
independently in the time I had, so the diff here is just going to be
complex and contian two distinct changes - sorry 🙁

frontend/src/desktop/components/AppProviders.tsx

@@ -1,15 +1,66 @@
-import { ReactNode } from "react";
+import { ReactNode, useEffect, useState } from "react";
 import { AppProviders as ProprietaryAppProviders } from "@proprietary/components/AppProviders";
 import { DesktopConfigSync } from '@app/components/DesktopConfigSync';
 import { DesktopBannerInitializer } from '@app/components/DesktopBannerInitializer';
+import { SetupWizard } from '@app/components/SetupWizard';
+import { useFirstLaunchCheck } from '@app/hooks/useFirstLaunchCheck';
+import { useBackendInitializer } from '@app/hooks/useBackendInitializer';
 import { DESKTOP_DEFAULT_APP_CONFIG } from '@app/config/defaultAppConfig';
+import { connectionModeService } from '@desktop/services/connectionModeService';
+import { tauriBackendService } from '@app/services/tauriBackendService';
 
 /**
  * Desktop application providers
  * Wraps proprietary providers and adds desktop-specific configuration
  * - Enables retry logic for app config (needed for Tauri mode when backend is starting)
+ * - Shows setup wizard on first launch
  */
 export function AppProviders({ children }: { children: ReactNode }) {
+  const { isFirstLaunch, setupComplete } = useFirstLaunchCheck();
+  const [connectionMode, setConnectionMode] = useState<'offline' | 'server' | null>(null);
+
+  // Load connection mode on mount
+  useEffect(() => {
+    void connectionModeService.getCurrentMode().then(setConnectionMode);
+  }, []);
+
+  // Initialize backend health monitoring for server mode
+  useEffect(() => {
+    if (setupComplete && !isFirstLaunch && connectionMode === 'server') {
+      console.log('[AppProviders] Initializing external backend monitoring for server mode');
+      void tauriBackendService.initializeExternalBackend();
+    }
+  }, [setupComplete, isFirstLaunch, connectionMode]);
+
+  // Only start bundled backend if in offline mode and setup is complete
+  const shouldStartBackend = setupComplete && !isFirstLaunch && connectionMode === 'offline';
+  useBackendInitializer(shouldStartBackend);
+
+  // Show setup wizard on first launch
+  if (isFirstLaunch && !setupComplete) {
+    return (
+      <ProprietaryAppProviders
+        appConfigRetryOptions={{
+          maxRetries: 5,
+          initialDelay: 1000,
+        }}
+        appConfigProviderProps={{
+          initialConfig: DESKTOP_DEFAULT_APP_CONFIG,
+          bootstrapMode: 'non-blocking',
+          autoFetch: false,
+        }}
+      >
+        <SetupWizard
+          onComplete={() => {
+            // Reload the page to reinitialize with new connection config
+            window.location.reload();
+          }}
+        />
+      </ProprietaryAppProviders>
+    );
+  }
+
+  // Normal app flow
   return (
     <ProprietaryAppProviders
       appConfigRetryOptions={{