An animation is a timeline of rows over one asset, played on an object rather than worn as a picture (#97)

Part (a) of the animation rework: model, commands, saving, runtime and nodes.

- AnimationAsset holds a root (sprite, text, container or scene) and rows; a row keys one
  property of the root or of an object inside it, keys sit on whole frames.
- The last key decides the length (its frame counts as a frame of its own). The playhead runs
  between frames, so numbers and colors blend every tick even at 10 fps; everything else holds.
- Playback gains `once-reset`, which puts back what was there before the start. A row can be
  relative, adding to where its target stood.
- Play / Pause / Stop animation act on an object; each instance plays on its own, the later
  start wins on a shared property, and a behavior writing the same property still writes last.
- A sprite no longer wears an animation through `texture`. "Create animation from texture"
  builds a sprite plus a texture row keyed frame by frame instead.
- The Animation tab shows a placeholder until the timeline editor (part b) lands.

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

src/editor/debugHook.ts

@@ -461,11 +461,8 @@ export function installDebugHook(app: Application, state: EditorState, editor: E
       rect: () => textureEditor.canvasRect(),
     },
     animation: {
-      /** Frames, the one on screen, play state and where the preview picture is drawn. */
-      current: () => editor.animationEditor.canvas.debugInfo(),
-      tileCentre: (index: number) => editor.animationEditor.canvas.tileCentre(index),
-      playButton: () => centreOf(editor.animationEditor.playButton),
-      playLabel: () => editor.animationEditor.playButton.text,
+      current: () => editor.animationEditor.currentAssetId,
+      info: () => editor.animationEditor.shownInfo,
     },
     container: {
       current: () => containerEditor.currentAssetId,