Let editors define FAQ topics freely instead of a hard-coded map

Elternbeirat.Contracts/Faq.cs

@@ -42,11 +42,16 @@ public record Faq
     public required string Answer { get; init; }
 
     /// <summary>
-    ///     Gets the topic the question is grouped under, e.g. <c>"mensa"</c>.
+    ///     Gets the topic the question is grouped under, e.g.
+    ///     <c>"Mensa und Mittagessen"</c>.
     /// </summary>
     /// <remarks>
     ///     <see langword="required"/>: the FAQ page groups entries by topic, so an entry
     ///     without one has no place. The field is required in PocketBase.
+    ///
+    ///     This is the heading shown on the page verbatim, not a slug: editors add a
+    ///     new group by typing its heading here, no code change. Entries with the same
+    ///     topic text land in one group.
     /// </remarks>
     [JsonPropertyName("topic")]
     public required string Topic { get; init; }