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/Editor.ts

@@ -1,4 +1,5 @@
 import type { Application } from 'pixi.js';
+import type { AssetType } from '../core/model/AssetTypes';
 import { findAsset, findObjectHolder } from '../core/model/Project';
 import type { ProjectStore } from '../core/store/ProjectStore';
 import type { TextureStore } from '../core/store/TextureStore';
@@ -52,6 +53,17 @@ const TAB_LABELS: Record<CentreTab, string> = {
   list: 'List',
 };
 
+/** Where an opened asset goes; a placeable one (sprite, camera, text, collider) has no tab of its own. */
+const TAB_OF_ASSET: Partial<Record<AssetType, CentreTab>> = {
+  scene: 'scene',
+  behavior: 'graph',
+  statemachine: 'statemachine',
+  shader: 'shader',
+  texture: 'texture',
+  animation: 'animation',
+  container: 'container',
+};
+
 const MIN_LEFT_WIDTH = 160;
 const MAX_LEFT_WIDTH = 500;
 const MIN_RIGHT_WIDTH = 200;
@@ -222,17 +234,18 @@ export class Editor implements PlayHost {
     });
     app.ticker.add((ticker) => this.tick(ticker.deltaMS / 1000));
     // A node, a frame and a template object exist only in their own tab, so selecting one
-    // switches to it; selecting the behavior, texture or container asset itself does not. A state
-    // machine or shader asset does switch (user's choice): its tab is the only place it shows anything.
+    // switches to it. Selecting an asset never does: that is what opening it (double-click,
+    // Enter, creating it) is for – see the `open` event below.
     state.on('selection', () => {
       const s = state.selection;
-      const machine = state.selectedStateMachineId !== null;
-      const shader = state.selectedShaderId !== null;
-      if (s?.kind === 'node' && !machine && !shader && this.tab !== 'graph') this.showTab('graph');
-      if ((s?.kind === 'node' || s?.kind === 'asset') && machine && this.tab !== 'statemachine')
-        this.showTab('statemachine');
-      if ((s?.kind === 'node' || s?.kind === 'asset') && shader && this.tab !== 'shader')
-        this.showTab('shader');
+      if (s?.kind === 'node') {
+        const tab = state.selectedStateMachineId
+          ? 'statemachine'
+          : state.selectedShaderId
+            ? 'shader'
+            : 'graph';
+        if (this.tab !== tab) this.showTab(tab);
+      }
       if (s?.kind === 'frame' && this.tab !== 'texture') this.showTab('texture');
       if (
         s?.kind === 'object' &&
@@ -241,6 +254,12 @@ export class Editor implements PlayHost {
       )
         this.showTab('container');
     });
+    state.on('open', () => {
+      const s = state.selection;
+      const tab =
+        s?.kind === 'asset' ? TAB_OF_ASSET[findAsset(state.project, s.assetId)?.type ?? 'sprite'] : undefined;
+      if (tab) this.showTab(tab);
+    });
     // Opening a list is a request to look at it, so this switches even when the slot is unchanged.
     state.on('list', () => {
       if (state.listSlot) this.showTab('list');