Fix email confirmation redirect missing basePath

- Use NEXT_PUBLIC_APP_URL instead of window.location.origin
- Ensures email confirmation redirects to /leopost/auth/callback/

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/components/auth/register-form.tsx

@@ -50,11 +50,14 @@ export function RegisterForm() {
       return
     }
 
+    // Use configured APP_URL to include basePath in redirect
+    const appUrl = process.env.NEXT_PUBLIC_APP_URL || window.location.origin
+
     const { error: signUpError } = await supabase.auth.signUp({
       email,
       password,
       options: {
-        emailRedirectTo: `${window.location.origin}/auth/callback`,
+        emailRedirectTo: `${appUrl}/auth/callback/`,
       }
     })