Group FAQs by a topic relation, ordered; drop unused FAQ teaser

Elternbeirat.Contracts/Faq.cs

@@ -6,7 +6,9 @@ namespace Elternbeirat.Contracts;
 ///     A single question and answer of the FAQ, as stored in PocketBase.
 /// </summary>
 /// <remarks>
-///     On the FAQ page, entries are grouped by <see cref="Topic"/>.
+///     On the FAQ page, entries are grouped by their <see cref="Topic"/>. The topic is
+///     a PocketBase relation; <see cref="Topic"/> is the resolved topic record, present
+///     only when the query expanded the relation (see <see cref="FaqExpand"/>).
 /// </remarks>
 public record Faq
 {
@@ -42,17 +44,39 @@ public record Faq
     public required string Answer { get; init; }
 
     /// <summary>
-    ///     Gets the topic the question is grouped under, e.g.
-    ///     <c>"Mensa und Mittagessen"</c>.
+    ///     Gets the expanded relations returned by PocketBase, or <see langword="null"/>
+    ///     when the query did not expand any.
+    /// </summary>
+    [JsonPropertyName("expand")]
+    public FaqExpand? Expand { get; init; }
+
+    /// <summary>
+    ///     Gets the resolved topic this entry is grouped under, or <see langword="null"/>
+    ///     when the query did not expand the topic relation.
     /// </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.
+    ///     Convenience over <see cref="Expand"/>: the FAQ page reads the grouping
+    ///     heading from here. It is <see langword="null"/> unless the entry was loaded
+    ///     with the topic relation expanded.
     /// </remarks>
+    [JsonIgnore]
+    public FaqTopic? Topic => Expand?.Topic;
+}
+
+/// <summary>
+///     The relations of a <see cref="Faq"/> that PocketBase returns under
+///     <c>expand</c> when the query asks for them.
+/// </summary>
+/// <remarks>
+///     One property per expandable relation, named after its PocketBase field, so the
+///     JSON <c>expand</c> object maps straight onto it. <see cref="Faq.Topic"/> reads
+///     through this.
+/// </remarks>
+public record FaqExpand
+{
+    /// <summary>
+    ///     Gets the expanded topic of the <c>topic</c> relation, if it was expanded.
+    /// </summary>
     [JsonPropertyName("topic")]
-    public required string Topic { get; init; }
+    public FaqTopic? Topic { get; init; }
 }