Replace chapter setting with multi-select locations; add chapter character summary

Chapters now carry many Locations (new Tags-style entity with cross-referencing)
instead of a single free-text Setting field, with a Locations tab on the novel
for browsing them and seeing every chapter set at each one. Also surfaces the
distinct characters appearing in a chapter's beats, linked, under the beat/word
count on the outline tab.

tests/Novelly.Api.Tests/NovelAgentServiceTests.cs

@@ -12,7 +12,7 @@ public class NovelAgentServiceTests : ServiceTestFixture
     private NovelAgentToolset _toolset = null!;
 
     protected override void OnSetUp() =>
-        _toolset = new NovelAgentToolset(Novels, Characters, Arcs, Chapters, Beats, Tags, Questions, NullLogger<NovelAgentToolset>.Instance);
+        _toolset = new NovelAgentToolset(Novels, Characters, Arcs, Chapters, Beats, Tags, Locations, Questions, NullLogger<NovelAgentToolset>.Instance);
 
     private NovelAgentService BuildAgent(ScriptedModelClient model) => new(
         Db.Context,