feat: add group chat and mention-gating to channel adapters

Slack: add requireMention option, resolve bot user ID on connect.
Telegram: add group chat mention/reply-to-bot detection, strip @mention
from message text, default requireMention=true for groups.
WhatsApp: add allowedGroupIds for group chat support, mention detection
via mentionedIds and body text, strip bot mention from messages.

src/channels/slack/adapter.ts

@@ -22,6 +22,8 @@ export interface SlackAdapterConfig {
   signingSecret: string;
   /** Channel IDs to respond in. Empty = all channels. */
   allowedChannelIds?: string[];
+  /** Require bot mention to respond (default: false). */
+  requireMention?: boolean;
 }
 
 /** Minimal shape of a Slack message event from Bolt. */
@@ -49,6 +51,7 @@ export class SlackAdapter implements ChannelAdapter {
   private messageHandler?: (msg: InboundMessage) => void;
   private config: SlackAdapterConfig;
   private userNameCache: Map<string, string> = new Map();
+  private botUserId?: string;
 
   get status(): ChannelStatus {
     return this._status;
@@ -81,6 +84,15 @@ export class SlackAdapter implements ChannelAdapter {
       });
 
       await this.app.start();
+
+      // Resolve bot user ID for mention detection
+      try {
+        const authResult = await this.app.client.auth.test();
+        this.botUserId = authResult.user_id as string | undefined;
+      } catch {
+        console.warn('Slack: could not resolve bot user ID for mention detection');
+      }
+
       this._status = 'connected';
       console.log('Slack bot connected via Socket Mode');
     } catch (error) {
@@ -167,6 +179,15 @@ export class SlackAdapter implements ChannelAdapter {
       return;
     }
 
+    // Mention requirement
+    const requireMention = this.config.requireMention ?? false;
+    if (requireMention && this.botUserId) {
+      const mentionPattern = `<@${this.botUserId}>`;
+      if (!(message.text ?? '').includes(mentionPattern)) {
+        return;
+      }
+    }
+
     // Build peer ID: channelId:threadTs (thread-aware)
     const threadTs = message.thread_ts ?? message.ts ?? '';
     const peerId = `${channelId}:${threadTs}`;