Manifest for Linux; connect as Background app where Utility is refused

- manifest.vrmanifest: binary_path_linux and binary_path_linux_arm. The
  Steam Frame's SteamVR reads only binary_path_linux_arm.
- handleManifests(): connect as Utility app first (works without a running
  SteamVR, e.g. from the Windows installer); if SteamVR refuses Utility apps,
  as on the Steam Frame, connect as Background app. Fail right away on other
  errors instead of going through initializeOpenVR()'s retry loop.
- main(): check --graphics-api before connecting to OpenVR, so a wrong value
  fails right away.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/utils/setup.cpp

@@ -262,8 +262,26 @@ void forceRemoveApplicationManifest()
 [[noreturn]] void handleManifests( const bool installManifest,
                                    const bool removeManifest )
 {
-    openvr_init::initializeOpenVR(
-        openvr_init::OpenVrInitializationType::Utility );
+    // Connect as Utility app first: it works without a running SteamVR (e.g.
+    // from the Windows installer). The Steam Frame's SteamVR refuses Utility
+    // apps (VRInitError_Init_NotAvailableToUtilityApps); there, connect as
+    // Background app, which needs a running SteamVR and never starts it.
+    // VR_Init is called directly: initializeOpenVR() retries every error with
+    // waits, including the one expected here.
+    vr::EVRInitError initError = vr::VRInitError_None;
+    vr::VR_Init( &initError, vr::VRApplication_Utility );
+    if ( initError == vr::VRInitError_Init_NotAvailableToUtilityApps )
+    {
+        qInfo() << "SteamVR refuses Utility apps, connecting as Background "
+                   "app.";
+        vr::VR_Init( &initError, vr::VRApplication_Background );
+    }
+    if ( initError != vr::VRInitError_None )
+    {
+        qCritical() << "Failed to connect to SteamVR for manifest handling:"
+                    << vr::VR_GetVRInitErrorAsEnglishDescription( initError );
+        exit( ReturnErrorCode::OPENVR_INIT_ERROR );
+    }
 
     int exit_code = ReturnErrorCode::SUCCESS;
     try