fix: propagate document indexing errors to caller

Previously indexing failures were silently logged, returning success
even when the embedding model was not configured or Qdrant was down.
Now the error is returned to the frontend so the user sees it.

web/app/dashboard/agents/_components/edit.tsx

@@ -267,7 +267,6 @@ function AgentEditDialogBody({
   }
 
   function onFormError(errors: object) {
-    console.error("Agent form validation errors:", errors)
     const firstError = Object.values(errors).find(
       (e: unknown) => (e as { message?: string })?.message
     ) as { message?: string } | undefined