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/config/zod-schema.approvals.ts

@@ -0,0 +1,28 @@
+import { z } from "zod";
+
+const ExecApprovalForwardTargetSchema = z
+  .object({
+    channel: z.string().min(1),
+    to: z.string().min(1),
+    accountId: z.string().optional(),
+    threadId: z.union([z.string(), z.number()]).optional(),
+  })
+  .strict();
+
+const ExecApprovalForwardingSchema = z
+  .object({
+    enabled: z.boolean().optional(),
+    mode: z.union([z.literal("session"), z.literal("targets"), z.literal("both")]).optional(),
+    agentFilter: z.array(z.string()).optional(),
+    sessionFilter: z.array(z.string()).optional(),
+    targets: z.array(ExecApprovalForwardTargetSchema).optional(),
+  })
+  .strict()
+  .optional();
+
+export const ApprovalsSchema = z
+  .object({
+    exec: ExecApprovalForwardingSchema,
+  })
+  .strict()
+  .optional();