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

Elternbeirat.Web/Features/Events/EventCard.razor

@@ -0,0 +1,43 @@
+@*
+    One event as a card: calendar sheet on the left, title, time, place and note on
+    the right. With an Href the whole card is that link (home embed); without one it
+    is a plain card (events page) and offers the event as a calendar file instead.
+*@
+@if (Href is null)
+{
+    <div class="event-card">@Details</div>
+}
+else
+{
+    <a class="event-card event-card-link" href="@Href">@Details</a>
+}
+
+@code {
+    // The card's content, the same in both forms. A template, not a child component,
+    // so the wrapper above stays the only difference between the two.
+    private RenderFragment Details => @<text>
+        <CalendarSheet Value="Value.Start" />
+        <span class="event-details">
+            <span class="event-title">@Value.Title</span>
+            @* The sheet is hidden from screen readers; this is the date they hear. *@
+            <span class="visually-hidden"><EventDate Value="Value" /></span>
+            @if (Span.Length > 0)
+            {
+                <span class="event-meta"><Icon Name="clock" Size="16" /> @Span</span>
+            }
+            @if (!string.IsNullOrWhiteSpace(Value.Location))
+            {
+                <span class="event-meta"><Icon Name="map-pin" Size="16" /> @Value.Location</span>
+            }
+            @if (!string.IsNullOrWhiteSpace(Value.Note))
+            {
+                <span class="event-note">@Value.Note</span>
+            }
+            @* A link inside a link is invalid HTML, so only the plain card offers it. *@
+            @if (Href is null)
+            {
+                <a class="event-ics" href="@IcsHref"><Icon Name="calendar-plus" Size="16" /> In Kalender übernehmen</a>
+            }
+        </span>
+    </text>;
+}