Remove chapter-level POV character

Character assignment now lives on beats only, per batch-assign. Drops
Chapter.PovCharacterId (entity, contracts, service, agent/import/MCP
tools, web UI) and the backing column via migration.

src/Novelly.Api/Chapters/Chapter.cs

@@ -1,5 +1,6 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Builders;
 using Novelly.Api.Beats;
-using Novelly.Api.Characters;
 using Novelly.Api.Common;
 using Novelly.Api.Projects;
 using Novelly.Api.Tags;
@@ -18,9 +19,6 @@ public class Chapter
 
     public string? Summary { get; set; }
 
-    public Guid? PovCharacterId { get; set; }
-    public Character? PovCharacter { get; set; }
-
     public string? Setting { get; set; }
     public string? Notes { get; set; }
 
@@ -38,3 +36,13 @@ public class Chapter
 
     public List<Tag> Tags { get; set; } = [];
 }
+
+public class ChapterEntityTypeConfiguration : IEntityTypeConfiguration<Chapter>
+{
+    public void Configure(EntityTypeBuilder<Chapter> entity)
+    {
+        entity.Property(c => c.Title).IsRequired().HasMaxLength(300);
+        entity.Property(c => c.Status).HasConversion<string>().HasMaxLength(32);
+        entity.HasIndex(c => new { c.ProjectId, c.Number });
+    }
+}