Timeline keys can be copied and pasted at the playhead, duplicated with Ctrl+drag, and frames inserted or removed from a right-click menu (#102)

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/editor/state.ts

@@ -1,4 +1,4 @@
-import type { KeyRef } from '../core/commands/animationCommands';
+import type { KeyClipboard, KeyRef } from '../core/commands/animationCommands';
 import { type Command, CommandError } from '../core/commands/Command';
 import { CommandStack } from '../core/commands/CommandStack';
 import type { Asset, SceneAsset } from '../core/model/Asset';
@@ -182,6 +182,8 @@ export class EditorState {
   saveStatus: SaveStatus = 'saved';
   /** Last user-facing message (errors, hints). */
   notice = '';
+  /** Keys copied in the Animation tab (#102). Lives for the session, across animations and projects. */
+  keyClipboard: KeyClipboard | null = null;
   /** The real (saved) model and its undo stack while `project` is the play-mode copy. */
   private edit: { project: Project; commands: CommandStack } | null = null;