Add calendar next to newsletter — month view fed by schedule webhook

- Calendar card beside newsletter signup (2-column grid, stacks on mobile)
- Month navigation (prev/next), Monday-first week, today highlighted
- Event dots on days with entries + event list below the grid
- Normalizes schedule webhook response ({data:[]} or [{data:[]}])
- Bilingual DE/EN month names + weekday headers, re-renders on language toggle

index.html

@@ -395,6 +395,7 @@
     <!-- Newsletter Section (nur logged-in) -->
     <section class="section section-alt newsletter-section" id="newsletter-section" style="display:none;">
       <div class="container">
+      <div class="newsletter-calendar-grid">
         <div class="newsletter-card">
           <img src="https://images.unsplash.com/photo-1596526131083-e8c633c948d2?w=120&h=120&fit=crop&q=80" alt="Newsletter" class="newsletter-image" />
           <h2>
@@ -421,6 +422,28 @@
             </p>
           </div>
         </div>
+        <div class="calendar-card">
+          <div class="calendar-header">
+            <button type="button" class="calendar-nav" id="calendar-prev" aria-label="Monat zurück">&#8249;</button>
+            <div class="calendar-title" id="calendar-title">
+              <span class="hide-de">Kalender</span>
+              <span class="hide-en">Calendar</span>
+            </div>
+            <button type="button" class="calendar-nav" id="calendar-next" aria-label="Monat vor">&#8250;</button>
+          </div>
+          <div class="calendar-weekdays">
+            <span class="hide-de">Mo</span><span class="hide-de">Di</span><span class="hide-de">Mi</span><span class="hide-de">Do</span><span class="hide-de">Fr</span><span class="hide-de">Sa</span><span class="hide-de">So</span>
+            <span class="hide-en">Mo</span><span class="hide-en">Tu</span><span class="hide-en">We</span><span class="hide-en">Th</span><span class="hide-en">Fr</span><span class="hide-en">Sa</span><span class="hide-en">Su</span>
+          </div>
+          <div class="calendar-grid" id="calendar-grid"></div>
+          <div class="calendar-events" id="calendar-events">
+            <p class="calendar-events-hint">
+              <span class="hide-de">Termine werden geladen...</span>
+              <span class="hide-en">Loading events...</span>
+            </p>
+          </div>
+        </div>
+      </div>
       </div>
     </section>