fix: 移除 staticcheck S1005 警告的多余 blank identifier

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/internal/pkg/apicompat/anthropic_to_responses.go

@@ -431,7 +431,7 @@ func normalizeToolParameters(schema json.RawMessage) json.RawMessage {
 		return schema
 	}
 
-	typ, _ := m["type"]
+	typ := m["type"]
 	if string(typ) != `"object"` {
 		return schema
 	}