Add genre feature; extract ConfirmModal for reusable confirm dialogs

Genres seed on boot, are editable per project, and gate agent config
errors more gracefully. ConfirmModal replaces ad-hoc confirm prompts
across chapters, tags, and characters pages.

src/Novelly.Api/Genres/GenreContracts.cs

@@ -0,0 +1,8 @@
+namespace Novelly.Api.Genres;
+
+public record GenreResponse(Guid Id, string Name);
+
+public static class GenreMapping
+{
+    public static GenreResponse ToResponse(this Genre g) => new(g.Id, g.Name);
+}