Remove Scenes, group beats by multiple characters; strip comments repo-wide

Drop the Scene entity/grouping in favor of chapters carrying prose directly
and beats belonging to many characters. Add markdown editor + character
multi-select components to the web client. Remove all XML doc and inline
comments across the touched C#/TS/CSS files in favor of self-documenting
names, and record that convention in CLAUDE.md. Add .mcp.json (local MCP
server config, no secrets) and ignore .idea/.

src/Novelly.Api/Beats/Beat.cs

@@ -1,16 +1,9 @@
 using Novelly.Api.Chapters;
 using Novelly.Api.Characters;
-using Novelly.Api.Scenes;
 using Novelly.Api.Tags;
 
 namespace Novelly.Api.Beats;
 
-/// <summary>
-/// One row of a chapter's outline: a short label, who it belongs to, what happened, and
-/// what it sets up. Beats are the planning layer — flat and ordered within a chapter,
-/// with no nesting. A beat may optionally be grouped under the <see cref="Scene"/> that
-/// will eventually carry its prose.
-/// </summary>
 public class Beat
 {
     public Guid Id { get; set; } = Guid.NewGuid();
@@ -18,24 +11,14 @@ public class Beat
     public Guid ChapterId { get; set; }
     public Chapter? Chapter { get; set; }
 
-    /// <summary>Optional grouping: the scene this beat will be written into.</summary>
-    public Guid? SceneId { get; set; }
-    public Scene? Scene { get; set; }
-
-    /// <summary>Position within the chapter. Gaps are allowed.</summary>
     public int SortOrder { get; set; }
 
-    /// <summary>A three-to-five word handle for the beat, not a sentence.</summary>
     public string Title { get; set; } = string.Empty;
 
-    /// <summary>Whose beat this is. Optional — not every beat belongs to one person.</summary>
-    public Guid? CharacterId { get; set; }
-    public Character? Character { get; set; }
+    public List<Character> Characters { get; set; } = [];
 
-    /// <summary>The event itself.</summary>
     public string? WhatHappened { get; set; }
 
-    /// <summary>What it sets in motion — the hook into the next beat.</summary>
     public string? WhatsNext { get; set; }
 
     public List<Tag> Tags { get; set; } = [];