Asset panel: double-click opens the tab, single click only selects (#71)

One rule for every asset type: a click on an asset row selects it, a
double-click (or Enter, or creating it via +) opens its tab. Selection
alone still switches tabs only for nodes, frames and template objects.

- state.openAsset(id) = select + 'open' event; the editor maps the asset
  type to its tab via TAB_OF_ASSET. The two special clauses for state
  machine and shader assets in the selection handler are gone.
- Creating via + and importing a texture from the picker open the tab;
  paste/drop of an image only selects.
- 3 unit tests (event order, re-open of a selected asset, selection never
  fires open), 14 e2e checks in step 4.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/editor/panels/AssetPanel.ts

@@ -85,15 +85,14 @@ export class AssetPanel extends Panel {
 
   private createAsset(type: AssetType, name = ASSET_TYPE_LABELS[type], props: PropertyBag = {}): void {
     const command = new CreateAssetCommand(type, nextAssetName(this.state.project, name), props);
-    if (this.state.execute(command)) this.state.select({ kind: 'asset', assetId: command.asset.id });
+    if (this.state.execute(command)) this.state.openAsset(command.asset.id);
   }
 
   /** One undo step for the asset and its frames. */
   private createAnimation(texture: TextureAsset): void {
     const create = new CreateAssetCommand('animation', nextAssetName(this.state.project, texture.name));
     const frames = new AddAnimationFramesCommand(create.asset.id, framesOfTexture(texture));
-    if (this.state.execute(oneStep(create.label, [create, frames])))
-      this.state.select({ kind: 'asset', assetId: create.asset.id });
+    if (this.state.execute(oneStep(create.label, [create, frames]))) this.state.openAsset(create.asset.id);
   }
 
   /**
@@ -108,10 +107,11 @@ export class AssetPanel extends Panel {
     openImagePicker({ state: this.state, textures: this.textures });
   }
 
-  /** Double-click / Enter on a scene makes it the active one. Placing is a drag, not a click. */
+  /** Double-click / Enter opens the asset's tab; a scene also becomes the active one. Placing is a drag. */
   private activate(id: string): void {
     const asset = findAsset(this.state.project, id);
     if (asset?.type === 'scene') this.state.execute(new SetActiveSceneCommand(id));
+    this.state.openAsset(id);
   }
 
   /** Where an asset's row sits on screen, so a check can pick it up by id (test hook). */