Improve local startup checks and Korean STT defaults

src/services/llm.ts

@@ -1,5 +1,6 @@
 import type { ConversationMemory, UserUtterance } from "./conversation.js";
 
 export interface LlmService {
+  warmup?(): Promise<void>;
   generateReply(memory: ConversationMemory, utterance: UserUtterance): Promise<string>;
 }