Post-launch email polish

• ✨ New: One-click email unsubscribe link (HMAC-protected) on every email we send. Resubscribe is one click as well.
• ✨ New: Public landing page redesign at app.orderrules.com.
• 🚀 Improved: All outbound emails now come from @orderrules.com addresses with a working Reply-To: support@orderrules.com.
• 🚀 Improved: Welcome and activation emails now link to the correct docs at www.orderrules.com/docs.
• 🚀 Improved: Daily summary, weekly digest, and monthly report emails now run reliably via Vercel Cron (replacing the previous external scheduler that was failing).