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/store/serialize.ts

@@ -6,7 +6,17 @@ import type { PropertyBag, PropertyValue } from '../model/Properties';
 import { PROJECT_FORMAT_VERSION, type Project } from '../model/Project';
 import type { SceneObject } from '../model/SceneObject';
 import { hasParentCycle } from '../model/walk';
-import { coerceValue, COMMON_PROPS, isCommonProp, type PropertyDef, type PropertySchema, schemaFor, VARIABLE_KINDS, variableDef, type VariableKind } from '../properties/PropertySchema';
+import {
+  coerceValue,
+  COMMON_PROPS,
+  isCommonProp,
+  type PropertyDef,
+  type PropertySchema,
+  schemaFor,
+  VARIABLE_KINDS,
+  variableDef,
+  type VariableKind,
+} from '../properties/PropertySchema';
 
 /**
  * Turns untrusted JSON (server file, import) into a well-formed Project. Unknown keys are
@@ -44,7 +54,14 @@ export function deserializeProject(raw: unknown, fallbackId = ''): Project {
     if (type === 'scene' || type === 'container') {
       assets.push({ id, type, name, props, objects: normalizeObjects(a.objects, schemas) });
     } else if (type === 'behavior') {
-      assets.push({ id, type, name, props, variables: variables.get(id) ?? [], graph: normalizeGraph(a.graph) });
+      assets.push({
+        id,
+        type,
+        name,
+        props,
+        variables: variables.get(id) ?? [],
+        graph: normalizeGraph(a.graph),
+      });
     } else {
       assets.push({ id, type, name, props });
     }
@@ -107,12 +124,14 @@ function normalizeVariables(raw: unknown): PropertyDef[] {
   for (const item of Array.isArray(raw) ? raw : []) {
     const v = asRecord(item);
     const key = typeof v.key === 'string' ? v.key : '';
-    const kind = (VARIABLE_KINDS as readonly string[]).includes(String(v.kind)) ? (v.kind as VariableKind) : 'number';
+    const kind = (VARIABLE_KINDS as readonly string[]).includes(String(v.kind))
+      ? (v.kind as VariableKind)
+      : 'number';
     // Common property keys are reserved – a variable of that name would shadow the switch.
     if (!/^[A-Za-z_][A-Za-z0-9_]*$/.test(key) || seen.has(key) || isCommonProp(key)) continue;
     seen.add(key);
     const def = variableDef(key, kind);
-    def.default = coerceValue(def, (v.default ?? def.default) as PropertyValue) as never;
+    def.default = coerceValue(def, (v.default ?? def.default) as PropertyValue);
     defs.push(def);
   }
   return defs;
@@ -130,7 +149,8 @@ function normalizeGraph(raw: unknown): Graph {
     nodeIds.add(id);
     const params: PropertyBag = {};
     for (const [key, value] of Object.entries(asRecord(n.params))) {
-      if (typeof value === 'number' || typeof value === 'string' || typeof value === 'boolean') params[key] = value;
+      if (typeof value === 'number' || typeof value === 'string' || typeof value === 'boolean')
+        params[key] = value;
     }
     const node: GraphNode = { id, type, x: toNumber(n.x), y: toNumber(n.y), params };
     graph.nodes.push(node);
@@ -142,10 +162,20 @@ function normalizeGraph(raw: unknown): Graph {
     const to = asRecord(e.to);
     const id = typeof e.id === 'string' ? e.id : '';
     if (!id || edgeIds.has(id)) continue;
-    if (typeof from.node !== 'string' || typeof from.port !== 'string' || typeof to.node !== 'string' || typeof to.port !== 'string') continue;
+    if (
+      typeof from.node !== 'string' ||
+      typeof from.port !== 'string' ||
+      typeof to.node !== 'string' ||
+      typeof to.port !== 'string'
+    )
+      continue;
     if (!nodeIds.has(from.node) || !nodeIds.has(to.node)) continue;
     edgeIds.add(id);
-    const edge: GraphEdge = { id, from: { node: from.node, port: from.port }, to: { node: to.node, port: to.port } };
+    const edge: GraphEdge = {
+      id,
+      from: { node: from.node, port: from.port },
+      to: { node: to.node, port: to.port },
+    };
     graph.edges.push(edge);
   }
   return graph;