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>

tests/core/serialize.test.ts

@@ -17,11 +17,22 @@ describe('serialize', () => {
         name: 'Broken',
         activeSceneId: 'missing',
         assets: [
-          { id: 's1', type: 'scene', name: 'Scene', props: { backgroundColor: '#000000', junk: 1 }, objects: [
-            { id: 'o1', assetId: 'sp1', position: { x: '5', y: null }, overrides: { color: '#00ff00', width: -3, foo: 1 } },
-            { id: 'o2', assetId: 'nope', position: {} },
-            { id: 'o3', assetId: 's1', position: {} },
-          ] },
+          {
+            id: 's1',
+            type: 'scene',
+            name: 'Scene',
+            props: { backgroundColor: '#000000', junk: 1 },
+            objects: [
+              {
+                id: 'o1',
+                assetId: 'sp1',
+                position: { x: '5', y: null },
+                overrides: { color: '#00ff00', width: -3, foo: 1 },
+              },
+              { id: 'o2', assetId: 'nope', position: {} },
+              { id: 'o3', assetId: 's1', position: {} },
+            ],
+          },
           { id: 'sp1', type: 'sprite', props: { width: 10 } },
           { id: 'x', type: 'texture' },
           { type: 'camera' },