Fix issue with saving AI model selection in settings

Update `saveOpenrouterMutation` in `client/src/pages/settings.tsx` to conditionally include `apiKey` in the payload only if it's not empty, resolving the bug where AI model selection was not persisting.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: ae4037a0-2a6f-4530-9bac-79b543286bda
Replit-Commit-Checkpoint-Type: intermediate_checkpoint
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/397bca8c-984f-43ff-841a-10897aeb8140/ae4037a0-2a6f-4530-9bac-79b543286bda/4KAFpKS

client/src/pages/settings.tsx

@@ -79,12 +79,19 @@ export default function Settings() {
   });
 
   const saveOpenrouterMutation = useMutation({
-    mutationFn: () => 
-      apiRequest('POST', '/api/openrouter/config', {
-        apiKey: openrouterApiKey,
+    mutationFn: () => {
+      const payload: any = {
         model: openrouterModel,
         systemPrompt: openrouterSystemPrompt,
-      }),
+      };
+      
+      // N'inclure apiKey que s'il n'est pas vide
+      if (openrouterApiKey && openrouterApiKey.trim() !== "") {
+        payload.apiKey = openrouterApiKey;
+      }
+      
+      return apiRequest('POST', '/api/openrouter/config', payload);
+    },
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: ['/api/openrouter/config'] });
       toast({