refactor: use random_int() for email change verification codes

Replace mt_rand/rand with random_int for stronger randomness guarantees
in verification code generation and Blade component keying.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/Unit/InsecurePrngArchTest.php

@@ -0,0 +1,17 @@
+<?php
+
+/**
+ * Architecture tests to prevent use of insecure PRNGs in application code.
+ *
+ * mt_rand() and rand() are not cryptographically secure. Use random_int()
+ * or random_bytes() instead for any security-sensitive context.
+ *
+ * @see GHSA-33rh-4c9r-74pf
+ */
+arch('app code must not use mt_rand')
+    ->expect('App')
+    ->not->toUse(['mt_rand', 'mt_srand']);
+
+arch('app code must not use rand')
+    ->expect('App')
+    ->not->toUse(['rand', 'srand']);