- Implemented the complete first-run experience:

Account creation and guarded onboarding flow.
Current-cash starting balance with automatic rollover enabled.
Dynamic bill generation, shared/custom categories, recurring targets, 
and optional same-day onboarding transactions.
Optional dormant reserve and additional categories.
Mailgun email or authenticator-app 2FA configuration.
Responsive dark/light UI with no overflow at 390px.
Fixed administrator session-ID creation bug.
Core implementation: [OnboardingService.php (line 
59)](/Users/tyemeclifford/Documents/GH/budget/app/OnboardingService.php:59), 
[onboarding.php (line 
19)](/Users/tyemeclifford/Documents/GH/budget/views/onboarding.php:19), 
and [index.php (line 
143)](/Users/tyemeclifford/Documents/GH/budget/public/index.php:143).
Verification passed: financial self-test, onboarding integration test, 
full browser walkthrough, mobile layout, routing guards, and zero 
browser console errors. Live email delivery requires actual Mailgun 
credentials and was not sent during testing.

app/Mailgun.php

@@ -52,7 +52,7 @@ final class Mailgun
         preg_match('/\s(\d{3})\s/', $statusLine, $matches);
         $status = (int) ($matches[1] ?? 500);
         if ($response === false || $status >= 400) {
-            throw new RuntimeException('Mailgun rejected the reminder: ' . ($response ?: $statusLine));
+            throw new RuntimeException('Mailgun rejected the message: ' . ($response ?: $statusLine));
         }
         return ['status' => $status, 'body' => $response];
     }