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/discord/monitor.ts

@@ -74,7 +74,11 @@ import {
   waitForDiscordGatewayStop,
 } from "./monitor.gateway.js";
 import { fetchDiscordApplicationId } from "./probe.js";
-import { reactMessageDiscord, sendMessageDiscord } from "./send.js";
+import {
+  reactMessageDiscord,
+  removeReactionDiscord,
+  sendMessageDiscord,
+} from "./send.js";
 import { normalizeDiscordToken } from "./token.js";
 
 export type MonitorDiscordOpts = {
@@ -958,6 +962,7 @@ export function createDiscordMessageHandler(params: {
         return;
       }
       const ackReaction = resolveAckReaction(cfg, route.agentId);
+      const removeAckAfterReply = cfg.messages?.removeAckAfterReply ?? false;
       const shouldAckReaction = () => {
         if (!ackReaction) return false;
         if (ackReactionScope === "all") return true;
@@ -972,6 +977,7 @@ export function createDiscordMessageHandler(params: {
         }
         return false;
       };
+      let didAddAckReaction = false;
       if (shouldAckReaction()) {
         reactMessageDiscord(message.channelId, message.id, ackReaction, {
           rest: client.rest,
@@ -980,6 +986,7 @@ export function createDiscordMessageHandler(params: {
             `discord react failed for channel ${message.channelId}: ${String(err)}`,
           );
         });
+        didAddAckReaction = true;
       }
 
       const fromLabel = isDirectMessage
@@ -1201,6 +1208,15 @@ export function createDiscordMessageHandler(params: {
           `discord: delivered ${finalCount} reply${finalCount === 1 ? "" : "ies"} to ${replyTarget}`,
         );
       }
+      if (removeAckAfterReply && didAddAckReaction && ackReaction) {
+        removeReactionDiscord(message.channelId, message.id, ackReaction, {
+          rest: client.rest,
+        }).catch((err) => {
+          logVerbose(
+            `discord: failed to remove ack reaction from ${message.channelId}/${message.id}: ${String(err)}`,
+          );
+        });
+      }
       if (
         isGuildMessage &&
         shouldClearHistory &&