feat: add removeAckAfterReply option for Discord, Slack, and Telegram

Add `messages.removeAckAfterReply` config option to automatically remove
acknowledgment reactions after the bot sends a reply, reducing visual
clutter while still providing immediate feedback.

Platforms: Discord, Slack, Telegram

Implementation:
- Added removeAckAfterReply boolean field to MessagesConfig (default: false)
- Track ack reaction state in all three platform handlers
- Remove ack reaction after successful reply delivery
- Graceful error handling with verbose logging

Platform-specific:
- Discord: uses removeReactionDiscord()
- Slack: uses removeSlackReaction()
- Telegram: uses setMessageReaction() with empty array

Closes #627

src/config/types.ts

@@ -999,6 +999,8 @@ export type MessagesConfig = {
   ackReaction?: string;
   /** When to send ack reactions. Default: "group-mentions". */
   ackReactionScope?: "group-mentions" | "group-all" | "direct" | "all";
+  /** Remove ack reaction after reply is sent (default: false). */
+  removeAckAfterReply?: boolean;
 };
 
 export type CommandsConfig = {