Place assets by dragging them from the panel into the view

The context menu entry is gone; dragging replaces it entirely. The drop
target is the view under the pointer, not the active tab, so the same
gesture works for scenes and for container templates.

While dragging, an outline shows the footprint the object will have plus
a crosshair on its origin, turning red when the drop would be refused.
Preview and command share one function (placementRejection), so the
outline cannot promise something the drop then rejects.

A left-press used to select the list row immediately. Since the container
tab follows the selection, it switched to the very container being dragged
and every drop would have nested it inside itself. The list now selects on
release without a drag: picking something up is not the same as choosing it.

src/editor/debugHook.ts

@@ -10,7 +10,7 @@ import type { EditorState } from './state';
  * visible text and to read editor state.
  */
 export function installDebugHook(app: Application, state: EditorState, editor: Editor): void {
-  const { viewport, gameView, graphEditor, textureEditor, containerEditor, hierarchy } = editor;
+  const { viewport, gameView, graphEditor, textureEditor, containerEditor, hierarchy, assets } = editor;
   const centreOf = (widget: { getGlobalPosition(): { x: number; y: number }; w: number; h: number }) => {
     const p = widget.getGlobalPosition();
     return { x: p.x + widget.w / 2, y: p.y + widget.h / 2 };
@@ -139,6 +139,10 @@ export function installDebugHook(app: Application, state: EditorState, editor: E
     labelsDropped,
     viewportCenter: () => centreOf(viewport),
     viewportInfo: () => viewport.debugInfo(),
+    /** Where a dragged asset would land in the Scene tab, and why not when it may not. */
+    dropPreview: () => viewport.dropInfo(),
+    /** An asset row by id – two assets can share a name with the container picker's label. */
+    assetRow: (id: string) => assets.rowGlobal(id),
     gameInfo: () => gameView.debugInfo(),
     layerOf: (id: string) => viewport.layerOf(id),
     drawOrder: () => viewport.drawOrder(),
@@ -171,6 +175,7 @@ export function installDebugHook(app: Application, state: EditorState, editor: E
       rect: () => containerEditor.canvasRect(),
       /** Where a template object is drawn, so a check can click or sample it. */
       objectScreen: (id: string) => containerEditor.objectScreen(id),
+      dropPreview: () => containerEditor.dropInfo(),
     },
     world: () => editor.worldSnapshot(),
     /** Rows the hierarchy shows – collapsed subtrees are not in here. */