[front] - fix: ensure null safety in model provider configuration and…

… disable dropdown (#8461)

- Add a null check to the model provider configuration to prevent accessing properties on null
 - Disable the provider dropdown trigger to prevent users from changing the embedding provider without contact
 - Make the 'Change' button disabled to match the dropdown trigger's new disabled state

front/components/workspace/ProviderManagementModal.tsx

@@ -195,7 +195,7 @@ export function ProviderManagementModal({
       <div className="flex flex-row items-center gap-4 px-4 pt-4">
         <div className="text-sm font-semibold">Embedding Provider:</div>
         <NewDropdownMenu>
-          <NewDropdownMenuTrigger>
+          <NewDropdownMenuTrigger disabled>
             <Tooltip
               label="Please contact us if you are willing to change this setting."
               trigger={
@@ -208,6 +208,7 @@ export function ProviderManagementModal({
                   }
                   variant="outline"
                   size="sm"
+                  disabled
                 />
               }
             />