refactor: update company registration flow and email handling; switch to zod for validation

lib/validations/email.schema.ts

@@ -0,0 +1,7 @@
+import { z } from 'zod';
+
+export const emailSchema = z.object({
+  to: z.string().email(),
+  subject: z.string().min(1).max(200),
+  html: z.string().min(1).max(5000),
+});