Extract date rendering into per-feature Date components

Elternbeirat.Web/Features/Posts/PostDate.razor

@@ -0,0 +1,10 @@
+@*
+    Renders a post's calendar day as a <time> element: the ISO value in the
+    machine-readable datetime attribute, the German long form as visible text.
+    A <time> needs the day in both forms, so putting it here keeps every caller
+    to a single tag instead of repeating the two PostDateFormat calls.
+
+    The event counterpart is <EventDate>, which renders a point in time (with an
+    optional clock time and range) instead of a plain day.
+*@
+<time datetime="@PostDateFormat.Iso(Value)">@PostDateFormat.Display(Value)</time>