Add Terms and Conditions and marketing opt-in checkboxes to registration

Registration now requires agreeing to the Terms and Conditions and lets
users opt in to hear about future projects. The opt-in is persisted on
the user via a new marketing_opt_in column (migration included).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

migrations/Version20260704160000.php

@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+
+namespace DoctrineMigrations;
+
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+final class Version20260704160000 extends AbstractMigration
+{
+    public function getDescription(): string
+    {
+        return 'Add marketing_opt_in column to user table';
+    }
+
+    public function up(Schema $schema): void
+    {
+        $this->addSql('ALTER TABLE `user` ADD marketing_opt_in TINYINT(1) NOT NULL DEFAULT 0');
+    }
+
+    public function down(Schema $schema): void
+    {
+        $this->addSql('ALTER TABLE `user` DROP marketing_opt_in');
+    }
+}