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/ChapterContracts.cs

@@ -11,8 +11,6 @@ public record ChapterSummaryResponse(
     int Number,
     string Title,
     string? Summary,
-    Guid? PovCharacterId,
-    string? PovCharacterName,
     string? Setting,
     DraftStatus Status,
     int? TargetWordCount,
@@ -27,8 +25,6 @@ public record ChapterResponse(
     int Number,
     string Title,
     string? Summary,
-    Guid? PovCharacterId,
-    string? PovCharacterName,
     string? Setting,
     string? Notes,
     DraftStatus Status,
@@ -43,7 +39,6 @@ public record CreateChapterRequest(
     string Title,
     int? Number = null,
     string? Summary = null,
-    Guid? PovCharacterId = null,
     string? Setting = null,
     string? Notes = null,
     DraftStatus Status = DraftStatus.Planned,
@@ -57,11 +52,7 @@ public class CreateChapterRequestValidator : IModelValidator<CreateChapterReques
     {
         var result = new ValidationResult();
 
-        if (string.IsNullOrWhiteSpace(model.Title))
-            result.AddError("Title", "'Title' must not be empty.");
-        else if (model.Title.Length > 200)
-            result.AddError("Title", "'Title' must be 200 characters or fewer.");
-
+        result.AddRequiredTextErrors("Title", "Title", model.Title, 200);
         ChapterValidation.OptionalFields(model.Number, model.Summary, model.Setting, model.Notes, model.TargetWordCount, model.Prose, model.Tags, result);
 
         return result;
@@ -72,7 +63,6 @@ public record UpdateChapterRequest(
     string? Title = null,
     int? Number = null,
     string? Summary = null,
-    Guid? PovCharacterId = null,
     string? Setting = null,
     string? Notes = null,
     DraftStatus? Status = null,
@@ -86,14 +76,7 @@ public class UpdateChapterRequestValidator : IModelValidator<UpdateChapterReques
     {
         var result = new ValidationResult();
 
-        if (model.Title is not null)
-        {
-            if (model.Title.Length == 0)
-                result.AddError("Title", "'Title' can not be cleared — a chapter always needs one.");
-            else if (model.Title.Length > 200)
-                result.AddError("Title", "'Title' must be 200 characters or fewer.");
-        }
-
+        result.AddUnclearableTextErrors("Title", "Title", model.Title, "a chapter", 200);
         ChapterValidation.OptionalFields(model.Number, model.Summary, model.Setting, model.Notes, model.TargetWordCount, model.Prose, model.Tags, result);
 
         return result;
@@ -133,7 +116,7 @@ public static class ChapterMapping
 {
     public static ChapterResponse ToResponse(this Chapter c) => new(
         c.Id, c.ProjectId, c.Number, c.Title, c.Summary,
-        c.PovCharacterId, c.PovCharacter?.Name, c.Setting, c.Notes,
+        c.Setting, c.Notes,
         c.Status, c.TargetWordCount,
         [.. c.Beats.OrderBy(b => b.SortOrder).Select(b => b.ToResponse())],
         c.Prose, c.WordCount,
@@ -142,7 +125,7 @@ public static class ChapterMapping
 
     public static ChapterSummaryResponse ToSummaryResponse(this Chapter c) => new(
         c.Id, c.ProjectId, c.Number, c.Title, c.Summary,
-        c.PovCharacterId, c.PovCharacter?.Name, c.Setting, c.Status, c.TargetWordCount,
+        c.Setting, c.Status, c.TargetWordCount,
         c.Beats.Count, c.WordCount,
         [.. c.Tags.OrderBy(t => t.Name).Select(t => t.ToResponse())],
         c.UpdatedAt);