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/zod-schema.ts

@@ -603,6 +603,7 @@ const MessagesSchema = z
     ackReactionScope: z
       .enum(["group-mentions", "group-all", "direct", "all"])
       .optional(),
+    removeAckAfterReply: z.boolean().optional(),
   })
   .optional();