feat(FN-3588): add immediate wake controls for agent inbox and message API

The merge delivers four major bodies of work. The dominant theme is FN-3588, which adds an "immediate wake" override to the message inbox API, exposes it in the MailboxModal UI, and updates `agent-heartbeat.ts` and `executor.ts` to honor the override alongside timer/signal triggers. FN-3705 gates re

Fusion-Task-Id: FN-3588

packages/dashboard/app/api/legacy.ts

@@ -7613,6 +7613,7 @@ export interface SendMessageInput {
   content: string;
   type: MessageType;
   metadata?: MessageMetadata;
+  wakeImmediately?: boolean;
 }
 
 /** Fetch inbox messages for the current user. */