feat: show speaker nickname instead of raw user ID in voice logs

Resolve the Discord user ID to a server nickname / global name (cached) and
display that in the transcript channel + console logs.

bot/src/voice.ts

@@ -81,6 +81,9 @@ export class VoiceSession {
    *  diagnosable. `note` says why (e.g. "음성 아님(VAD 차단)", "너무 짧음", "ok"). */
   onTurn?: (info: {
     user: string;
+    /** Resolved display name (server nickname / global name) for the speaker,
+     *  so logs show a human name instead of the raw Discord user ID. */
+    userName?: string;
     transcript: string;
     reply: string;
     note?: string;
@@ -164,6 +167,31 @@ export class VoiceSession {
     });
   }
 
+  /** Resolve a speaker's Discord user ID to a human display name (server
+   *  nickname, else global name / username), cached so we don't refetch every
+   *  utterance. Falls back to the ID if lookup fails. */
+  private nameCache = new Map<string, string>();
+  private async displayName(userId: string): Promise<string> {
+    const cached = this.nameCache.get(userId);
+    if (cached) return cached;
+    let name = userId;
+    try {
+      const guild: any = this.client?.guilds?.cache?.get(this.guildId);
+      let member: any = guild?.members?.cache?.get(userId);
+      if (!member && guild?.members?.fetch) member = await guild.members.fetch(userId).catch(() => null);
+      if (member) {
+        name = member.displayName || member.nickname || member.user?.globalName || member.user?.username || userId;
+      } else {
+        const u: any = this.client?.users?.cache?.get(userId) || (await this.client?.users?.fetch?.(userId).catch(() => null));
+        name = u?.globalName || u?.username || userId;
+      }
+    } catch {
+      /* fall back to id */
+    }
+    this.nameCache.set(userId, name);
+    return name;
+  }
+
   private async captureUtterance(userId: string): Promise<void> {
     // Don't start a new capture once we're tearing down (user left).
     if (this.destroyed) return;
@@ -199,6 +227,7 @@ export class VoiceSession {
     if (mono.length < DISCORD_RATE * 0.3 * 2) {
       this.onTurn?.({
         user: userId,
+        userName: await this.displayName(userId),
         transcript: "",
         reply: "",
         note: "너무 짧음(<300ms)",
@@ -247,6 +276,7 @@ export class VoiceSession {
       // explains why a turn did or didn't answer, with full stage timing.
       this.onTurn?.({
         user: userId,
+        userName: await this.displayName(userId),
         transcript: metaSeen?.transcript ?? "",
         reply: metaSeen?.reply ?? "",
         note: metaSeen?.note,