Fix newsletter signup flow requiring the email address twice

Priority: High

Problem

The newsletter signup flow at https://mantoshkumar1.github.io/newsletter/ appears to require a visitor to enter their email address twice during subscription. This is confusing and creates unnecessary friction; it was confusing even during owner testing.

Goal

Understand exactly why the duplicate email-entry step occurs and reduce the signup flow to the simplest safe experience Buttondown supports.

Scope

• Reproduce the full subscription flow from the website.
• Identify which step is controlled by this repository versus Buttondown.
• Determine whether the second email-entry step is required, configurable, or avoidable.
• Review the redirect/confirmation flow for unnecessary or unclear steps.
• Preserve double opt-in if required for consent/deliverability; the objective is to remove duplicate data entry, not weaken confirmation.
• Test the final flow on desktop and mobile.

Acceptance criteria

• The current signup flow is documented step by step.
• The reason the email must currently be entered twice is identified.
• Duplicate email entry is removed if technically possible without weakening opt-in safety.
• If Buttondown requires it, the UI clearly explains what is happening and why.
• A first-time visitor can subscribe without confusion on desktop and mobile.

Start by reproducing the signup flow at https://mantoshkumar1.github.io/newsletter/ on desktop and mobile, documenting each step. Trace which steps belong to this repository and which are controlled by Buttondown, then review the redirect and confirmation flow. Done means duplicate entry is removed where safe, or the required step is clearly explained without weakening double opt-in.