feat(discord): add exec approval forwarding to DMs (#1621)

* feat(discord): add exec approval forwarding to DMs

Add support for forwarding exec approval requests to Discord DMs,
allowing users to approve/deny command execution via interactive buttons.

Features:
- New DiscordExecApprovalHandler that connects to gateway and listens
  for exec.approval.requested/resolved events
- Sends DMs with embeds showing command details and 3 buttons:
  Allow once, Always allow, Deny
- Configurable via channels.discord.execApprovals with:
  - enabled: boolean
  - approvers: Discord user IDs to notify
  - agentFilter: only forward for specific agents
  - sessionFilter: only forward for matching session patterns
- Updates message embed when approval is resolved or expires

Also fixes exec completion routing: when async exec completes after
approval, the heartbeat now uses a specialized prompt to ensure the
model relays the result to the user instead of responding HEARTBEAT_OK.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* feat: generic exec approvals forwarding (#1621) (thanks @czekaj)

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
Co-authored-by: Peter Steinberger <steipete@gmail.com>

src/gateway/server.impl.ts

@@ -43,6 +43,7 @@ import {
 import { startGatewayDiscovery } from "./server-discovery-runtime.js";
 import { ExecApprovalManager } from "./exec-approval-manager.js";
 import { createExecApprovalHandlers } from "./server-methods/exec-approval.js";
+import { createExecApprovalForwarder } from "../infra/exec-approval-forwarder.js";
 import type { startBrowserControlServerIfEnabled } from "./server-browser.js";
 import { createChannelManager } from "./server-channels.js";
 import { createAgentEventHandler } from "./server-chat.js";
@@ -396,7 +397,10 @@ export async function startGatewayServer(
   void cron.start().catch((err) => logCron.error(`failed to start: ${String(err)}`));
 
   const execApprovalManager = new ExecApprovalManager();
-  const execApprovalHandlers = createExecApprovalHandlers(execApprovalManager);
+  const execApprovalForwarder = createExecApprovalForwarder();
+  const execApprovalHandlers = createExecApprovalHandlers(execApprovalManager, {
+    forwarder: execApprovalForwarder,
+  });
 
   const canvasHostServerPort = (canvasHostServer as CanvasHostServer | null)?.port;