Add newsletter / email signup

[AmitoVrito]

Description

Add an email signup form for release announcements.

What to do

• Add in footer or dedicated section
• Options: Buttondown, Substack, Mailchimp, or ConvertKit
• Keep it simple — just email + subscribe button
• GDPR compliant

[AmitoVrito]

Thanks for your interest! I will assign it to you. Before you start, could you give the repo a ⭐ on the main repo (https://github.com/SynapseKit/SynapseKit)? It really helps with visibility for a new project. Looking forward to your PR!