Add character aliases/identity links, move-beats, keyboard help overlay

- Characters can carry aliases and be linked as the same underlying
  person (canonical SameCharacterAsId, optional reveal chapter/note),
  surfaced through the API, MCP tools, agent toolset, and web UI.
- Characters page redesigned as a filterable/sortable table (name+
  aliases, role, importance, occupation, tags) instead of a sidebar
  list, to stay usable as the cast grows.
- Beats can be moved between chapters (BeatService.MoveAsync + MCP/
  agent tool + endpoint).
- Add a keyboard-shortcuts help overlay (HelpButton/HelpOverlayContext)
  wired into the project layout.
- CLAUDE.md: require every frontend component to carry a unique id
  attribute; apply it to CharacterMultiSelect and MarkdownEditor.

src/Novelly.Api/Characters/Character.cs

@@ -1,6 +1,7 @@
 using Microsoft.EntityFrameworkCore;
 using Microsoft.EntityFrameworkCore.Metadata.Builders;
 using Novelly.Api.Beats;
+using Novelly.Api.Chapters;
 using Novelly.Api.Projects;
 using Novelly.Api.Tags;
 
@@ -38,6 +39,16 @@ public class Character
 
     public string? Notes { get; set; }
 
+    public List<string> Aliases { get; set; } = [];
+
+    public Guid? SameCharacterAsId { get; set; }
+    public Character? SameCharacterAs { get; set; }
+    public List<Character> OtherIdentities { get; set; } = [];
+
+    public Guid? RevealedInChapterId { get; set; }
+    public Chapter? RevealedInChapter { get; set; }
+    public string? IdentityNote { get; set; }
+
     public DateTimeOffset CreatedAt { get; set; } = DateTimeOffset.UtcNow;
     public DateTimeOffset UpdatedAt { get; set; } = DateTimeOffset.UtcNow;
 
@@ -72,12 +83,19 @@ public class CharacterEntityTypeConfiguration : IEntityTypeConfiguration<Charact
         entity.Property(c => c.Role).HasConversion<string>().HasMaxLength(32);
         entity.Property(c => c.Importance).HasConversion<string>().HasMaxLength(32);
         entity.HasIndex(c => c.ProjectId);
+        entity.HasIndex(c => c.SameCharacterAsId);
 
         entity.HasMany(c => c.Relationships).WithOne(r => r.Character!)
             .HasForeignKey(r => r.CharacterId).OnDelete(DeleteBehavior.Cascade);
 
         entity.HasMany(c => c.ArcStages).WithOne(s => s.Character!)
             .HasForeignKey(s => s.CharacterId).OnDelete(DeleteBehavior.Cascade);
+
+        entity.HasOne(c => c.SameCharacterAs).WithMany(c => c.OtherIdentities)
+            .HasForeignKey(c => c.SameCharacterAsId).OnDelete(DeleteBehavior.SetNull);
+
+        entity.HasOne(c => c.RevealedInChapter).WithMany()
+            .HasForeignKey(c => c.RevealedInChapterId).OnDelete(DeleteBehavior.SetNull);
     }
 }