Add Bedienungsanleitung (user guide) and link from admin dashboard

- Static HTML guide at /bedienungsanleitung.html with DATACREW logo
- Fixed image paths and anchor links for standalone hosting
- Added "Hilfe" link in admin bar (opens guide in new tab)

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

src/app/admin/dashboard/page.tsx

@@ -242,12 +242,22 @@ export default function AdminDashboardPage() {
           <span className="text-[11px] bg-primary/8 text-primary px-2 py-0.5 rounded-md font-semibold uppercase tracking-wider">
             Admin
           </span>
-          <button
-            onClick={handleLogout}
-            className="text-xs text-text-muted hover:text-danger transition-colors font-medium"
-          >
-            Abmelden
-          </button>
+          <div className="flex items-center gap-3">
+            <a
+              href="/bedienungsanleitung.html"
+              target="_blank"
+              rel="noopener"
+              className="text-xs text-text-muted hover:text-accent transition-colors font-medium"
+            >
+              Hilfe
+            </a>
+            <button
+              onClick={handleLogout}
+              className="text-xs text-text-muted hover:text-danger transition-colors font-medium"
+            >
+              Abmelden
+            </button>
+          </div>
         </div>
       </div>