chore: Improve prefill router error reporting and fix typo (#4220)

Co-authored-by: Claude <noreply@anthropic.com>

lib/llm/src/kv_router/prefill_router.rs

@@ -249,7 +249,10 @@ impl
                 next.generate(decode_request).await
             }
             Err(e) => {
-                tracing::debug!(error = %e, "Remote prefill failed, falling back to decode-only");
+                tracing::warn!(
+                    error = %e,
+                    "Remote prefill failed, falling back to decode-only. This may impact performance in disaggregated deployments. Verify prefill workers are healthy and accessible."
+                );
                 next.generate(context.map(|_| req)).await
             }
         }

lib/llm/src/kv_router/scheduler.rs

@@ -42,7 +42,7 @@ pub struct PotentialLoad {
 
 #[derive(Debug, thiserror::Error)]
 pub enum KvSchedulerError {
-    #[error("no endpoints aviailable to route work")]
+    #[error("no endpoints available to route work")]
     NoEndpoints,
 
     #[error("all workers busy")]