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/slack/monitor.ts

@@ -59,7 +59,7 @@ import {
 } from "../routing/session-key.js";
 import type { RuntimeEnv } from "../runtime.js";
 import { resolveSlackAccount } from "./accounts.js";
-import { reactSlackMessage } from "./actions.js";
+import { reactSlackMessage, removeSlackReaction } from "./actions.js";
 import { sendMessageSlack } from "./send.js";
 import { resolveSlackThreadTargets } from "./threading.js";
 import { resolveSlackAppToken, resolveSlackBotToken } from "./token.js";
@@ -913,6 +913,7 @@ export async function monitorSlackProvider(opts: MonitorSlackOpts = {}) {
     const rawBody = (message.text ?? "").trim() || media?.placeholder || "";
     if (!rawBody) return;
     const ackReaction = resolveAckReaction(cfg, route.agentId);
+    const removeAckAfterReply = cfg.messages?.removeAckAfterReply ?? false;
     const shouldAckReaction = () => {
       if (!ackReaction) return false;
       if (ackReactionScope === "all") return true;
@@ -927,6 +928,7 @@ export async function monitorSlackProvider(opts: MonitorSlackOpts = {}) {
       }
       return false;
     };
+    let didAddAckReaction = false;
     if (shouldAckReaction() && message.ts) {
       reactSlackMessage(message.channel, message.ts, ackReaction, {
         token: botToken,
@@ -936,6 +938,7 @@ export async function monitorSlackProvider(opts: MonitorSlackOpts = {}) {
           `slack react failed for channel ${message.channel}: ${String(err)}`,
         );
       });
+      didAddAckReaction = true;
     }
 
     const roomLabel = channelName ? `#${channelName}` : `#${message.channel}`;
@@ -1157,6 +1160,16 @@ export async function monitorSlackProvider(opts: MonitorSlackOpts = {}) {
         `slack: delivered ${finalCount} reply${finalCount === 1 ? "" : "ies"} to ${replyTarget}`,
       );
     }
+    if (removeAckAfterReply && didAddAckReaction && ackReaction && message.ts) {
+      removeSlackReaction(message.channel, message.ts, ackReaction, {
+        token: botToken,
+        client: app.client,
+      }).catch((err) => {
+        logVerbose(
+          `slack: failed to remove ack reaction from ${message.channel}/${message.ts}: ${String(err)}`,
+        );
+      });
+    }
   };
 
   app.event(