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/ui/widgets/Button.ts

@@ -34,7 +34,9 @@ export class Button extends Widget {
     this.addChild(this.bg, this.labelText);
 
     // Leaving while pressed cancels the click: a release elsewhere must not activate.
-    this.trackHover(() => { this.pressed = false; });
+    this.trackHover(() => {
+      this.pressed = false;
+    });
     this.on('pointerdown', (e: FederatedPointerEvent) => {
       if (e.button !== 0) return;
       this.pressed = true;
@@ -89,10 +91,22 @@ export class Button extends Widget {
     const flat = this.variant === 'default' || this.variant === 'ghost';
     let fill: number | null = c.control;
     let border: number | null = c.border;
-    if (this.variant === 'primary') { fill = c.accent; border = null; }
-    if (this.variant === 'danger') { fill = c.danger; border = null; }
-    if (this.variant === 'ghost') { fill = null; border = null; }
-    if (this.toggled) { fill = c.accent; border = null; }
+    if (this.variant === 'primary') {
+      fill = c.accent;
+      border = null;
+    }
+    if (this.variant === 'danger') {
+      fill = c.danger;
+      border = null;
+    }
+    if (this.variant === 'ghost') {
+      fill = null;
+      border = null;
+    }
+    if (this.toggled) {
+      fill = c.accent;
+      border = null;
+    }
     if (this.hovered && !this.toggled && flat) fill = c.controlHover;
     if (this.pressed && flat) fill = c.controlActive;
     const stroke = this.focused ? c.accent : border;