Resilient prepare, Twitch chat echo, parallel chat startup

- Prepare endpoint wraps each destination in try/catch; partial success
  if at least one destination is ready (e.g., Twitch works when YouTube
  is rate-limited)
- Echo sent Twitch messages back to app WebSocket (IRC doesn't echo
  your own PRIVMSGs)
- Start YouTube and Twitch chat clients in parallel via Promise.allSettled
- Fix Twitch auth failure detection (Login unsuccessful + Login
  authentication failed)
- Add Twitch IRC debug logging

src/services/chat-manager.service.ts

@@ -111,13 +111,15 @@ export class ChatManager {
 
     this.sessions.set(sessionKey, session);
 
+    const chatPromises: Promise<void>[] = [];
     for (const dest of plan.destinations) {
       if (dest.serviceId === 'YOUTUBE' && dest.linkedAccountId) {
-        await this.startYouTubeChat(session, dest);
+        chatPromises.push(this.startYouTubeChat(session, dest));
       } else if (dest.serviceId === 'TWITCH' && dest.linkedAccountId) {
-        await this.startTwitchChat(session, dest);
+        chatPromises.push(this.startTwitchChat(session, dest));
       }
     }
+    await Promise.allSettled(chatPromises);
   }
 
   async handleSendMessage(
@@ -146,9 +148,42 @@ export class ChatManager {
     const twitchClient = session.twitchClients.get(destinationId);
     if (twitchClient) {
       twitchClient.sendMessage(text);
+      // Echo sent message back to app (Twitch IRC doesn't echo your own PRIVMSGs)
+      try {
+        const { account } = await getDecryptedToken(this.prisma, userId, destinationId);
+        this.sendEcho(session, 'TWITCH', destinationId, account.displayName, text);
+      } catch {
+        // Still echo with fallback name
+        this.sendEcho(session, 'TWITCH', destinationId, 'You', text);
+      }
     }
   }
 
+  private sendEcho(
+    session: ChatSession,
+    service: string,
+    destinationId: string,
+    authorName: string,
+    text: string,
+  ): void {
+    this.sendToSocket(session.socket, {
+      type: 'chat_message',
+      planId: session.planId,
+      service,
+      destinationId,
+      message: {
+        id: `echo-${Date.now()}-${Math.random().toString(36).substring(2, 8)}`,
+        authorName,
+        authorImageUrl: null,
+        text,
+        timestamp: Date.now(),
+        isModerator: false,
+        isBroadcaster: true,
+        color: null,
+      },
+    });
+  }
+
   async stopChat(planId: string, userId: string): Promise<void> {
     const sessionKey = `${userId}:${planId}`;
     const session = this.sessions.get(sessionKey);
@@ -345,6 +380,7 @@ export class ChatManager {
   }
 
   private async startTwitchChat(session: ChatSession, dest: any): Promise<void> {
+    this.logger.info({ planId: session.planId, destId: dest.linkedAccountId }, 'startTwitchChat called');
     try {
       const { account, accessToken } = await getDecryptedToken(
         this.prisma,