M3 Registrierung und Login-Grundlage ergänzen

- SaaS-Auth-Helper und PDO-Datenbankzugriff einführen
- Registrierung, Login, Logout und Kontoansicht ergänzen
- Auth-Migration, Flow-Check und Smoke-Abdeckung aktualisieren

konto.php

@@ -0,0 +1,50 @@
+<?php
+
+require_once __DIR__ . '/functions.php';
+
+$user = saas_require_login();
+
+include 'header.php';
+include 'headerline.php';
+include 'nav.php';
+?>
+
+<section id="banner">
+    <div class="content">
+        <h2>Kundenkonto</h2>
+
+        <?php if (isset($_GET['registered'])): ?>
+            <div class="hint-box success"><p>Das Kundenkonto wurde angelegt.</p></div>
+        <?php endif; ?>
+
+        <table>
+            <tr>
+                <th>Name</th>
+                <td><?php echo saas_html($user['display_name']); ?></td>
+            </tr>
+            <tr>
+                <th>E-Mail</th>
+                <td><?php echo saas_html($user['email']); ?></td>
+            </tr>
+            <tr>
+                <th>Kunde</th>
+                <td><?php echo saas_html($user['tenant_name']); ?></td>
+            </tr>
+            <tr>
+                <th>Kundenkuerzel</th>
+                <td><?php echo saas_html($user['tenant_slug']); ?></td>
+            </tr>
+            <tr>
+                <th>Rolle</th>
+                <td><?php echo saas_html($user['role']); ?></td>
+            </tr>
+        </table>
+
+        <form method="post" action="logout.php">
+            <?php echo app_csrf_field(); ?>
+            <button type="submit">Abmelden</button>
+        </form>
+    </div>
+</section>
+
+<?php include 'footer.php'; ?>