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/commands/variableCommands.ts

@@ -10,7 +10,11 @@ export class AddVariableCommand implements Command {
   readonly label: string;
   readonly def: PropertyDef;
 
-  constructor(private readonly assetId: string, key: string, kind: VariableKind) {
+  constructor(
+    private readonly assetId: string,
+    key: string,
+    kind: VariableKind,
+  ) {
     this.def = variableDef(key, kind);
     this.label = `Add variable ${key}`;
   }
@@ -18,7 +22,8 @@ export class AddVariableCommand implements Command {
   execute(project: Project): void {
     const asset = requireBehavior(project, this.assetId);
     if (!isValidVariableName(this.def.key)) throw new CommandError(INVALID_NAME);
-    if (asset.variables.some((v) => v.key === this.def.key)) throw new CommandError(`Variable "${this.def.key}" already exists`);
+    if (asset.variables.some((v) => v.key === this.def.key))
+      throw new CommandError(`Variable "${this.def.key}" already exists`);
     asset.variables.push(this.def);
     asset.props[this.def.key] = this.def.default;
   }
@@ -36,7 +41,10 @@ export class RemoveVariableCommand implements Command {
   private removed?: { def: Removed<PropertyDef>; value: PropertyValue | undefined };
   private overrides: { holderId: string; objectId: string; value: PropertyValue }[] = [];
 
-  constructor(private readonly assetId: string, private readonly key: string) {
+  constructor(
+    private readonly assetId: string,
+    private readonly key: string,
+  ) {
     this.label = `Remove variable ${key}`;
   }
 
@@ -75,7 +83,11 @@ export class RemoveVariableCommand implements Command {
 export class RenameVariableCommand implements Command {
   readonly label: string;
 
-  constructor(private readonly assetId: string, private readonly from: string, private readonly to: string) {
+  constructor(
+    private readonly assetId: string,
+    private readonly from: string,
+    private readonly to: string,
+  ) {
     this.label = `Rename variable ${from}`;
   }