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.

src/Novelly.Api/Data/NovelDbContext.cs

@@ -7,6 +7,7 @@ using Novelly.Api.Chapters;
 using Novelly.Api.Characters;
 using Novelly.Api.Genres;
 using Novelly.Api.Imports;
+using Novelly.Api.Locations;
 using Novelly.Api.Novels;
 using Novelly.Api.Questions;
 using Novelly.Api.Tags;
@@ -24,6 +25,7 @@ public class NovelDbContext(DbContextOptions<NovelDbContext> options) : Identity
     public DbSet<CharacterArcStage> CharacterArcStages => Set<CharacterArcStage>();
     public DbSet<Beat> Beats => Set<Beat>();
     public DbSet<Tag> Tags => Set<Tag>();
+    public DbSet<Location> Locations => Set<Location>();
     public DbSet<Chapter> Chapters => Set<Chapter>();
     public DbSet<OpenQuestion> OpenQuestions => Set<OpenQuestion>();
     public DbSet<AgentConversation> Conversations => Set<AgentConversation>();
@@ -51,6 +53,7 @@ public interface INovelDbContext
     DbSet<CharacterArcStage> CharacterArcStages { get; }
     DbSet<Beat> Beats { get; }
     DbSet<Tag> Tags { get; }
+    DbSet<Location> Locations { get; }
     DbSet<Chapter> Chapters { get; }
     DbSet<OpenQuestion> OpenQuestions { get; }
     DbSet<AgentConversation> Conversations { get; }