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/Project.ts

@@ -1,5 +1,4 @@
-import type { Asset, ContainerAsset, SceneAsset } from './Asset';
-import { isSceneAsset } from './Asset';
+import { type Asset, type ContainerAsset, isSceneAsset, type SceneAsset } from './Asset';
 import type { SceneObject } from './SceneObject';
 
 /** Written into every document. Reserved for format migrations – the loader does not branch on it yet. */
@@ -49,7 +48,10 @@ export interface SceneObjectRef {
 }
 
 /** Objects of all scenes and container templates that satisfy `predicate`, each with its holder. */
-export function objectsWhere(project: Project, predicate: (object: SceneObject) => boolean): SceneObjectRef[] {
+export function objectsWhere(
+  project: Project,
+  predicate: (object: SceneObject) => boolean,
+): SceneObjectRef[] {
   const result: SceneObjectRef[] = [];
   for (const holder of objectHolders(project)) {
     for (const object of holder.objects) if (predicate(object)) result.push({ holder, object });