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/properties/PropertySchema.ts

@@ -28,7 +28,9 @@ export type VariableKind = (typeof VARIABLE_KINDS)[number];
  * same goes for everything parented below it. Assets default to on, so switching a single
  * instance off is an ordinary override. Scenes have no such switch (they are not placed).
  */
-export const COMMON_PROPS: PropertySchema = [{ key: 'enabled', label: 'Enabled', kind: 'boolean', default: true }];
+export const COMMON_PROPS: PropertySchema = [
+  { key: 'enabled', label: 'Enabled', kind: 'boolean', default: true },
+];
 
 const COMMON_KEYS = new Set(COMMON_PROPS.map((d) => d.key));
 
@@ -91,7 +93,10 @@ const ASSET_SCHEMAS: Record<AssetType, PropertySchema> = {
 
 /** Type schema with the common properties in front – the effective schema of an asset type. */
 const FULL_SCHEMAS: Record<AssetType, PropertySchema> = Object.fromEntries(
-  (Object.keys(ASSET_SCHEMAS) as AssetType[]).map((type) => [type, type === 'scene' ? ASSET_SCHEMAS[type] : [...COMMON_PROPS, ...ASSET_SCHEMAS[type]]]),
+  (Object.keys(ASSET_SCHEMAS) as AssetType[]).map((type) => [
+    type,
+    type === 'scene' ? ASSET_SCHEMAS[type] : [...COMMON_PROPS, ...ASSET_SCHEMAS[type]],
+  ]),
 ) as Record<AssetType, PropertySchema>;
 
 /** Schema shared by every asset of a type (common properties first). */

src/core/properties/bounds.ts

@@ -25,7 +25,10 @@ export function textSize(props: PropertyBag): { w: number; h: number } {
   const size = Math.max(1, Number(props.fontSize ?? TEXT_DEFAULTS.fontSize));
   const lines = String(props.text ?? TEXT_DEFAULTS.text).split('\n');
   const longest = lines.reduce((max, line) => Math.max(max, line.length), 0);
-  return { w: Math.max(size * CHAR_WIDTH, longest * size * CHAR_WIDTH), h: lines.length * size * LINE_HEIGHT };
+  return {
+    w: Math.max(size * CHAR_WIDTH, longest * size * CHAR_WIDTH),
+    h: lines.length * size * LINE_HEIGHT,
+  };
 }
 
 /** Horizontal anchor of a text object: 0 = left edge on the position, 0.5 = centred, 1 = right. */

src/core/properties/camera.ts

@@ -17,7 +17,10 @@ export interface WorldRect {
  */
 export function cameraFrame(props: PropertyBag): { w: number; h: number } {
   const zoom = Math.max(0.01, Number(props.zoom ?? DEFAULTS.zoom));
-  return { w: Number(props.width ?? DEFAULTS.width) / zoom, h: Number(props.height ?? DEFAULTS.height) / zoom };
+  return {
+    w: Number(props.width ?? DEFAULTS.width) / zoom,
+    h: Number(props.height ?? DEFAULTS.height) / zoom,
+  };
 }
 
 export function rectAround(cx: number, cy: number, w: number, h: number): WorldRect {

src/core/properties/collider.ts

@@ -19,8 +19,20 @@ export type PlaneAxis = 'x' | 'y';
 
 /** The shape described by collider properties, centred on `centre` (a world position). */
 export function colliderShape(props: PropertyBag, centre: Vec2): ColliderShape {
-  if (props.shape === 'circle') return { kind: 'circle', x: centre.x, y: centre.y, r: Math.max(0, Number(props.radius ?? DEFAULTS.radius)) };
-  return { kind: 'box', x: centre.x, y: centre.y, w: Math.max(0, Number(props.width ?? DEFAULTS.width)), h: Math.max(0, Number(props.height ?? DEFAULTS.height)) };
+  if (props.shape === 'circle')
+    return {
+      kind: 'circle',
+      x: centre.x,
+      y: centre.y,
+      r: Math.max(0, Number(props.radius ?? DEFAULTS.radius)),
+    };
+  return {
+    kind: 'box',
+    x: centre.x,
+    y: centre.y,
+    w: Math.max(0, Number(props.width ?? DEFAULTS.width)),
+    h: Math.max(0, Number(props.height ?? DEFAULTS.height)),
+  };
 }
 
 /** Whether the collider only reports overlaps (true) or also blocks movement (false). */
@@ -36,7 +48,8 @@ export function colliderSize(props: PropertyBag): { w: number; h: number } {
 
 /** Whether a point lies inside a shape (used for pointer hit tests). */
 export function shapeContains(shape: ColliderShape, point: Vec2): boolean {
-  if (shape.kind === 'circle') return (point.x - shape.x) ** 2 + (point.y - shape.y) ** 2 <= shape.r * shape.r;
+  if (shape.kind === 'circle')
+    return (point.x - shape.x) ** 2 + (point.y - shape.y) ** 2 <= shape.r * shape.r;
   return Math.abs(point.x - shape.x) * 2 <= shape.w && Math.abs(point.y - shape.y) * 2 <= shape.h;
 }
 
@@ -86,7 +99,12 @@ export function axisSeparation(a: ColliderShape, b: ColliderShape, axis: PlaneAx
  * `axis` so it just touches `obstacle` (0 when they do not overlap). Only valid when
  * `mover` approached from the far side, i.e. it did not overlap before its move.
  */
-export function axisCorrection(mover: ColliderShape, obstacle: ColliderShape, axis: PlaneAxis, dir: 1 | -1): number {
+export function axisCorrection(
+  mover: ColliderShape,
+  obstacle: ColliderShape,
+  axis: PlaneAxis,
+  dir: 1 | -1,
+): number {
   if (!shapesOverlap(mover, obstacle)) return 0;
   return Math.max(0, dir * (mover[axis] - obstacle[axis]) + axisSeparation(mover, obstacle, axis));
 }

src/core/properties/enabled.ts

@@ -16,7 +16,11 @@ function propsEnabled(props: PropertyBag): boolean {
  * Whether `start` and every ancestor of it are switched on. Generic over the shape so the
  * model (scene objects), the viewport (draw items) and the runtime (entities) share one rule.
  */
-export function enabledAlongChain<T>(start: T, propsOf: (item: T) => PropertyBag, parentOf: (item: T) => T | null): boolean {
+export function enabledAlongChain<T>(
+  start: T,
+  propsOf: (item: T) => PropertyBag,
+  parentOf: (item: T) => T | null,
+): boolean {
   for (const item of parentChain(start, parentOf)) if (!propsEnabled(propsOf(item))) return false;
   return true;
 }