feat(marketing-pages): sendWelcomeEmail job + handler enqueues it

sendWelcomeEmailJob takes IMailerService, validates the typed input
(userId + email), and delegates to mailer.sendWelcome. The
onAuthUserSignedUpHandler now takes IJobQueue and enqueues
"marketing-pages.send-welcome-email" with the event payload.

Both binders bind a RecordingMailerService at the IMailerService
symbol (production placeholder until a real adapter ships) and pass
mailer / queue into the wrapped factories. Dev-seed additionally
queue.register()s the slug so the in-memory queue dispatches via
the wrapped job; production relies on the generated Payload event-task
to resolve the wrapped handler from the container.

packages/marketing-pages/src/jobs/send-welcome-email.job.ts

@@ -0,0 +1,20 @@
+// packages/marketing-pages/src/jobs/send-welcome-email.job.ts
+import { z } from "zod";
+import type { IMailerService } from "../application/services/mailer.service.interface";
+
+export const sendWelcomeEmailInputSchema = z
+  .object({
+    userId: z.string(),
+    email: z.string().email(),
+  })
+  .strict();
+
+export type SendWelcomeEmailInput = z.infer<typeof sendWelcomeEmailInputSchema>;
+export type ISendWelcomeEmailJob = ReturnType<typeof sendWelcomeEmailJob>;
+
+export const sendWelcomeEmailJob =
+  (mailer: IMailerService) =>
+  async (input: SendWelcomeEmailInput): Promise<void> => {
+    sendWelcomeEmailInputSchema.parse(input);
+    await mailer.sendWelcome(input.userId, input.email);
+  };