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/editor/debugHook.ts

@@ -24,6 +24,9 @@ export function installDebugHook(app: Application, state: EditorState, editor: E
       for (const child of node.children) walk(child);
     };
     walk(app.stage);
+    // TypeScript does not track the assignment inside `walk`, so it believes `found` is still
+    // `null` here – hence both the disable and the cast below.
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (!found) return null;
     const node = found as Text;
     const p = node.getGlobalPosition();
@@ -43,7 +46,8 @@ export function installDebugHook(app: Application, state: EditorState, editor: E
     gameScreen: (id: string) => gameView.objectScreen(id),
     graph: {
       current: () => graphEditor.currentAssetId,
-      portAt: (nodeId: string, port: string, isOutput: boolean) => graphEditor.portGlobal(nodeId, port, isOutput),
+      portAt: (nodeId: string, port: string, isOutput: boolean) =>
+        graphEditor.portGlobal(nodeId, port, isOutput),
       nodeAt: (nodeId: string) => graphEditor.nodeGlobal(nodeId),
       center: () => centreOf(graphEditor),
     },