Nutzerverwaltung-Upgrade: 3 Rollen, Ordner-Zuweisung, Passwort-Aenderung

- 3 Rollen: admin (voll), user (permanent), client (30 Tage Ablauf)
- Ordner-basierte Bildzuweisung statt Einzelbilder (user_folders Tabelle)
- Root-Bilder oeffentlich, Unterordner nur fuer zugewiesene Nutzer
- Passwort-Aenderung fuer alle Nutzer (Self-Service + Admin)
- Admin kann beliebige Admins erstellen/loeschen
- Thumbnail-Generierung fuer Unterordner
- Admin-Dashboard komplett ueberarbeitet

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

index.html

@@ -130,6 +130,25 @@ layout: default
                         <li id="admin-link"></li>
                     </ul>
                 </form>
+                <div id="pw-change-section" style="display:none; margin-top:1.5em; border-top:1px solid rgba(255,255,255,0.2); padding-top:1.5em;">
+                    <h3>Passwort aendern</h3>
+                    <form id="pw-change-form">
+                        <div class="fields">
+                            <div class="field">
+                                <input type="password" id="pw-old" placeholder="Altes Passwort" required />
+                            </div>
+                            <div class="field half">
+                                <input type="password" id="pw-new" placeholder="Neues Passwort" required />
+                            </div>
+                            <div class="field half">
+                                <input type="password" id="pw-confirm" placeholder="Passwort bestaetigen" required />
+                            </div>
+                        </div>
+                        <ul class="actions">
+                            <li><input type="submit" value="Passwort aendern" class="primary" /></li>
+                        </ul>
+                    </form>
+                </div>
             </section>
         </div>
     </footer>