Add a Container tab and propagate template edits

The Container tab reuses SceneViewport against any object holder, so a
container template is edited exactly like a scene. Right-click no longer
changes the selection, which previously made nesting impossible: opening
the menu on a container loaded it, and "Place in container" then targeted
itself.

Template edits (move, rename, override) now reach already-placed instances
per slot, through a shared templateSync used by both the apply path and the
plain object commands. Copies the user has touched keep their own value.

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

src/editor/debugHook.ts

@@ -8,7 +8,7 @@ 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, hierarchy } = editor;
+  const { viewport, gameView, graphEditor, textureEditor, containerEditor, hierarchy } = 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 };
@@ -135,6 +135,14 @@ export function installDebugHook(app: Application, state: EditorState, editor: E
       /** Where an image pixel of the shown sheet sits on screen (frames are dragged in image coordinates). */
       pointAt: (x: number, y: number) => textureEditor.imageToScreen(x, y),
     },
+    container: {
+      current: () => containerEditor.currentAssetId,
+      pickerWidth: () => containerEditor.pickerWidth,
+      center: () => centreOf(containerEditor),
+      rect: () => containerEditor.canvasRect(),
+      /** Where a template object is drawn, so a check can click or sample it. */
+      objectScreen: (id: string) => containerEditor.objectScreen(id),
+    },
     world: () => editor.worldSnapshot(),
     /** Rows the hierarchy shows – collapsed subtrees are not in here. */
     hierarchyOrder: () => hierarchy.rowOrder(),