docs(skills): update whisper skill with correct transcription priority

Clarify that local whisper is the primary provider (free, offline),
OpenAI API is the fallback, and the skill only activates when both
are unavailable. Add setup instructions noting no restart is required.

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

src/channels/manager.ts

@@ -265,8 +265,6 @@ export class ChannelManager {
       // Keep heartbeat acknowledgements internal (same behavior as desktop/gateway stream path).
       if (isHeartbeatAckEvent(event)) {
         if (event.type === "message_end") {
-          this.stopTyping();
-          this.removeAckReaction();
           this.aggregator = null;
         }
         return;