Add soft delete + trash, keyboard-first web overhaul, move chapter tags to bottom

Adds SoftDelete/Trash across characters, chapters, locations, beats with a
purge schedule and Trash page. Reworks the web client for keyboard-driven
navigation (focus helpers, help overlay, keyboard.md doc). Moves the
ChapterPage tag editor to the bottom of the page to match CharacterDetailPage.

src/Novelly.Api/Chapters/Chapter.cs

@@ -8,7 +8,7 @@ using Novelly.Api.Tags;
 
 namespace Novelly.Api.Chapters;
 
-public class Chapter
+public class Chapter : ISoftDeletable
 {
     public Guid Id { get; set; } = Guid.NewGuid();
     public Guid NovelId { get; set; }
@@ -33,6 +33,7 @@ public class Chapter
 
     public DateTimeOffset CreatedAt { get; set; } = DateTimeOffset.UtcNow;
     public DateTimeOffset UpdatedAt { get; set; } = DateTimeOffset.UtcNow;
+    public DateTimeOffset? DeletedAt { get; set; }
 
     public List<Beat> Beats { get; set; } = [];
 
@@ -48,5 +49,6 @@ public class ChapterEntityTypeConfiguration : IEntityTypeConfiguration<Chapter>
         entity.Property(c => c.Status).HasConversion<string>().HasMaxLength(32);
         entity.Property(c => c.Kind).HasConversion<string>().HasMaxLength(32);
         entity.HasIndex(c => new { c.NovelId, c.Number });
+        entity.HasQueryFilter(c => c.DeletedAt == null);
     }
 }