Add events calendar with ICS feed and switch content naming to English

Elternbeirat.Web/Services/Post.cs

@@ -1,8 +1,8 @@
 namespace Elternbeirat.Web.Services;
 
 /// <summary>
-/// A news post ("Beitrag"), read from a Markdown file in
-/// <c>Content/beitraege/</c>. Unlike a <see cref="Page"/>, a post has a date and
+/// A news post, read from a Markdown file in <c>Content/posts/</c>. Unlike a
+/// <see cref="Page"/>, a post has a date and
 /// is shown in a chronological list. The file name (without extension) is the
 /// slug.
 /// </summary>