Add post and event cards, shared calendar sheet and per-event ICS; rework past events and next-event card

Elternbeirat.Web/Features/Embeds/EventsEmbed.razor

@@ -6,16 +6,8 @@
         <ul class="event-list">
             @foreach (var ev in _upcomingEvents)
             {
-                <li>
-                    <a class="card-link" href="/events">
-                        <span class="event-title">@ev.Title</span>
-                        <EventDate Value="ev" />
-                        @if (!string.IsNullOrWhiteSpace(ev.Location))
-                        {
-                            <span class="event-location">@ev.Location</span>
-                        }
-                    </a>
-                </li>
+                @* A teaser: each card leads to the events page with the full list. *@
+                <li><EventCard Value="ev" Href="/events" /></li>
             }
         </ul>
     </section>