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.providers-core.ts

@@ -244,6 +244,15 @@ export const DiscordAccountSchema = z
     dm: DiscordDmSchema.optional(),
     guilds: z.record(z.string(), DiscordGuildSchema.optional()).optional(),
     heartbeat: ChannelHeartbeatVisibilitySchema,
+    execApprovals: z
+      .object({
+        enabled: z.boolean().optional(),
+        approvers: z.array(z.union([z.string(), z.number()])).optional(),
+        agentFilter: z.array(z.string()).optional(),
+        sessionFilter: z.array(z.string()).optional(),
+      })
+      .strict()
+      .optional(),
   })
   .strict();