Show step durations only where one is set

Three of the four Ablauf steps had no duration and therefore rendered a
red "[Dauer?]" placeholder. Requested: drop those, keep the "2–3 Tage"
on step 03.

The span is now only rendered when step.dauer is filled, instead of
falling back to a placeholder. Each .ablauf-step is its own grid, so the
auto-width third column simply collapses and the text takes the space -
no layout shift. The editor label no longer claims that an empty field
produces a placeholder.

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

admin/lib/schema.js

@@ -206,7 +206,7 @@ module.exports = [
           { key: 'num', label: 'Nummer', type: 'text' },
           { key: 'title', label: 'Titel', type: 'text' },
           { key: 'text', label: 'Text', type: 'textarea' },
-          { key: 'dauer', label: 'Dauer (leer = Platzhalter)', type: 'text' },
+          { key: 'dauer', label: 'Dauer (leer = wird nicht angezeigt)', type: 'text' },
         ],
       },
     ],

src/pages/index.astro

@@ -199,9 +199,7 @@ const { hero, warum, preis, highlights, leistungen, mappe, ablauf, about, faq, k
               <h3>{step.title}</h3>
               <p>{step.text}</p>
             </div>
-            <span class="ablauf-dauer">
-              {step.dauer || <span class="placeholder">[Dauer?]</span>}
-            </span>
+            {step.dauer && <span class="ablauf-dauer">{step.dauer}</span>}
           </div>
         ))}
       </div>