[Issue]: Make the confirmation email open the app

[anis022]

Branch Name

feature/native-deep-links

Description

Signup sends a confirmation email. The link in it opens the phone browser instead of the app. The person ends up signed in inside Safari or Chrome while the app still sits on the login screen. Nothing tells them to go back and sign in again, so most people will think it failed.

Scope

• Set up an app link on Android and a universal link on iOS for the Vercel domain
• A custom scheme is the fallback if the domain checks turn out to be too much work
• Point the Supabase redirect at it
• Handle the link once the app is open so it lands on the right page

Acceptance Criteria

• Tapping the link opens the app and not the browser
• The person lands signed in, not on the login screen
• The same link still works in a browser for people on the website

Notes

Both platforms need a small file served from the Vercel domain. iOS testing needs a Mac.

Checklist

• I have checked for duplicate issues.
• I have assigned the issue to the correct project board.
• I have tagged the issue properly.

Code of Conduct

• I agree to follow this project's Code of Conduct