Report graphics startup failures instead of aborting

When no backend could create a window and a WebGPU device, aurora hit
an ASSERT and the process aborted with only SDL's last error in the log.
Keep the first adapter, device or window error, return it from
aurora_initialize with a new initializationStatus, and have the runtime
throw it so the existing fatal popup and fatal log record the reason.

ImGui shutdown now skips backends that never initialized, so the
shutdown that follows a failed start does not crash.

From upstream patchzyy/Wiicompiled 6f14bde (#244, KartPad batch).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Wg7mB8ogCWmp9GH19Uc82B

aurora-main/lib/aurora.cpp

@@ -1229,15 +1229,23 @@ AuroraInfo initialize(int argc, char* argv[], const AuroraConfig& config) noexce
   const AuroraBackend requestedBackend = config.desiredBackend;
   AuroraBackend selectedBackend = requestedBackend;
   bool windowCreated = false;
+  std::string firstGraphicsError;
+  const auto rememberGraphicsError = [&] {
+    if (firstGraphicsError.empty() && SDL_GetError()[0] != '\0') {
+      firstGraphicsError = SDL_GetError();
+    }
+  };
   if (selectedBackend != BACKEND_AUTO) {
     Log.info("Requested graphics backend: {}", backend_name(selectedBackend));
     if (window::create_window(selectedBackend)) {
       if (webgpu::initialize(selectedBackend)) {
         windowCreated = true;
       } else {
+        rememberGraphicsError();
         window::destroy_window();
       }
     } else {
+      rememberGraphicsError();
       Log.error("Failed to create a window for backend {}: {}", backend_name(selectedBackend), SDL_GetError());
     }
     if (!windowCreated) {
@@ -1254,18 +1262,28 @@ AuroraInfo initialize(int argc, char* argv[], const AuroraConfig& config) noexce
     for (const auto backendType : PreferredBackendOrder) {
       selectedBackend = backendType;
       if (!window::create_window(selectedBackend)) {
+        rememberGraphicsError();
         continue;
       }
       if (webgpu::initialize(selectedBackend)) {
         windowCreated = true;
         break;
       } else {
+        rememberGraphicsError();
         window::destroy_window();
       }
     }
   }
 
-  ASSERT(windowCreated, "Error creating window: {}", SDL_GetError());
+  if (!windowCreated) {
+    if (firstGraphicsError.empty()) firstGraphicsError = "No supported graphics backend is available";
+    SDL_SetError("%s", firstGraphicsError.c_str());
+    Log.error("Graphics initialization failed: {}", firstGraphicsError);
+    return {
+        .initializationStatus = AURORA_INITIALIZATION_GRAPHICS_UNAVAILABLE,
+        .initializationError = SDL_GetError(),
+    };
+  }
   if (requestedBackend != BACKEND_AUTO && selectedBackend != requestedBackend) {
     Log.error(
         "Graphics backend fallback in effect: video.graphics_api requested {}, "