refactor: use .finally() to always delete limiter from Map

Address bot review feedback: use .finally() instead of .then()/.catch()
so limiters.delete() runs regardless of whether stop() succeeds or
throws (e.g. already stopped by concurrent 429).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

open-sse/services/rateLimitManager.ts

@@ -350,9 +350,9 @@ export function updateFromHeaders(provider, connectionId, headers, status, model
     // be hours for providers like Codex with long rate limit windows).
     // This lets upstream callers (e.g. LiteLLM) trigger fallback to other providers.
     // After stop, delete from Map so getLimiter() creates a fresh instance.
-    limiter.stop({ dropWaitingJobs: true }).then(() => {
+    limiter.stop({ dropWaitingJobs: true }).finally(() => {
       limiters.delete(limiterKey);
-    }).catch(() => {});
+    });
     return;
   }