Refactoring: one file per node, consistent comments, shared helpers, split large modules

- Graph: nodes.ts split into nodes/<category>/<Type>.ts (62 files) with
  shared.ts factories and index.ts registry; NodeContext/values/NodeRegistry
  separated, writeTyped() replaces duplicated typed writes
- Comments: one style (JSDoc on non-obvious exports, // for decisions and
  traps), wrong/stale comments fixed or removed, ids.ts now real 10 base-36 chars
- Core: chainOf, shared worldPosition/editorPosition core, commands/require.ts,
  commands/naming.ts, util/list.ts, setBagValue/toPosition/propDef; dead code
  removed (isBehaviorAsset, SCENE_OBJECT_SCHEMA, CommandStack.subscribe,
  Input.axis, setMode, titleText, World.worldPosition, unused ctor params)
- Editor: Inspector split into inspector/ sections, App.ts into Editor.ts +
  debugHook.ts + shortcuts.ts, Viewport into items.ts + symbols.ts, shared
  "Add collider" action, unified type labels/swatches
- UI toolkit: Widget.trackHover/onPointerRelease, drawControlBox, math helpers,
  Popup.openBelow, Menu/Dialog/ColorPicker/ListRow in own files, named Theme sizes
- Tools: seed-demo/smoke-demo and demo-check project removed, tools/lib
  (harness, projects, builders), e2e.mjs as runner over tools/e2e/*.mjs sections
- Tests: tests/helpers.ts replaces copied fixtures and NodeContext doubles

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/core/graph/nodes/variable/GetVariable.ts

@@ -0,0 +1,13 @@
+import type { NodeDef } from '../../NodeRegistry';
+import { any, variableParam } from '../shared';
+
+export const GetVariable: NodeDef = {
+  type: 'GetVariable',
+  label: 'Get variable',
+  category: 'variable',
+  description: "Reads one of this behavior's variables.",
+  inputs: [],
+  outputs: [any('value')],
+  params: [variableParam],
+  run: (ctx, _inputs, params) => ({ outputs: { value: ctx.variables[String(params.variable ?? '')] ?? null } }),
+};