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/state.ts

@@ -83,6 +83,8 @@ export type EditorEvent =
   | 'selection'
   /** The List tab was pointed at another list (or at none). */
   | 'list'
+  /** An asset was opened (double-click, Enter, or just created): its tab should show. */
+  | 'open'
   | 'mode'
   | 'save'
   | 'notice'
@@ -267,6 +269,16 @@ export class EditorState {
     this.emit('list');
   }
 
+  /**
+   * Selects the asset and asks for its tab. Selecting alone never switches tabs (a click in the
+   * Assets panel is a look at the inspector); this is the way a double-click or a fresh asset gets
+   * there, and like `openList` it works without knowing the `Editor`.
+   */
+  openAsset(assetId: string): void {
+    this.select({ kind: 'asset', assetId });
+    this.emit('open');
+  }
+
   select(selection: Selection): void {
     // Test hooks pass the short form `{ kind: 'object', holderId, objectId }` without `objectIds`.
     // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition