Add ESLint and Prettier, and close the node test gaps

Tooling:
- Prettier as the single formatting authority (110 columns, single quotes,
  measured against the existing style); Markdown excluded because table-cell
  padding turns the README glossary into 1000-character lines.
- Type-aware ESLint ending in eslint-config-prettier, so a rule always means
  "this is a bug", never "this looks different".
- .editorconfig and an `npm run check` that runs typecheck, lint, format and
  tests in one go.

Findings fixed on the first run: three more duplicate imports, four
String(unknown) calls (parameter types narrowed instead of casts), two dead
initialisers, two redundant casts, a console.log for a real error. Two
warnings were false here and are disabled with a reason in place.

Tests 132 -> 269:
- node-catalog.test.ts covers every node with a run(), with a guard that fails
  when a new node has no row.
- behavior-events.test.ts covers the ten event nodes through a running World,
  checking timing rather than existence.
- Input's state machine (press/release/releaseAll) is reachable without DOM
  events now; the DOM handlers are thin adapters.

Compare fell back to == without a configured operator although the schema
default is <; aligned.

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

src/core/model/container.ts

@@ -16,7 +16,11 @@ export interface TemplateLink {
  * asset holds the template this object was instantiated from. Undefined for everything else
  * (no template id, or the link is stale).
  */
-export function templateLinkOf(project: Project, tree: ObjectTree, object: SceneObject): TemplateLink | undefined {
+export function templateLinkOf(
+  project: Project,
+  tree: ObjectTree,
+  object: SceneObject,
+): TemplateLink | undefined {
   if (!object.templateId) return undefined;
   for (const containerObject of chainOf(tree, object).slice(1)) {
     const asset = findAsset(project, containerObject.assetId);
@@ -46,12 +50,19 @@ const MAX_NESTING = 8;
  * turn – unless the template already spells its content out (that is what a container built
  * from a selection containing another container does).
  */
-export function instantiateContainer(project: Project, asset: ContainerAsset, containerObjectId: string, depth = 0): SceneObject[] {
+export function instantiateContainer(
+  project: Project,
+  asset: ContainerAsset,
+  containerObjectId: string,
+  depth = 0,
+): SceneObject[] {
   const ids = new Map(asset.objects.map((t) => [t.id, newId()]));
   const result: SceneObject[] = [];
   for (const template of asset.objects) {
     const id = ids.get(template.id)!;
-    const parentId = template.parentId ? ids.get(template.parentId) ?? containerObjectId : containerObjectId;
+    const parentId = template.parentId
+      ? (ids.get(template.parentId) ?? containerObjectId)
+      : containerObjectId;
     result.push({
       id,
       assetId: template.assetId,