Let a value be a bundle of named fields

PropertyValue was number | string | boolean | list. A struct joins it, which
costs two things the typechecker found rather than I did.

An object on a data edge used to mean a live entity, so asEntity would have
taken a struct for one and asString would have read .name off it. EntityHandle
now carries a symbol brand – a symbol so no field name can impersonate it, and
it never serializes, which suits a thing that exists only while the game runs.
It is built in exactly one place.

String(value) would have written a struct as [object Object] at 39 call sites.
They go through textOf(), which is identical for primitives.

normalizeGraph dropped everything but primitives from node params, so the List
node lost its value on every save ([3,1,4] round-tripped to undefined).
Variables were spared: they have a schema, params have none.

src/core/model/texture.ts

@@ -1,5 +1,5 @@
 import type { TextureAsset, TextureFrame } from './Asset';
-import type { PropertyBag } from './Properties';
+import { type PropertyBag, textOf } from './Properties';
 import { findAsset, type Project } from './Project';
 
 /** Mirrors `TextureStore::isValidName` on the server, where the name is derived from the bytes. */
@@ -56,7 +56,7 @@ export function textureRefIds(asset: TextureAsset): string[] {
 }
 
 export function resolveTexture(project: Project, props: PropertyBag): TextureRef | null {
-  const id = String(props.texture ?? '');
+  const id = textOf(props.texture ?? '');
   if (!id) return null;
   const asset = findAsset(project, id);
   if (asset) return asset.type === 'texture' ? refFor(asset, null) : null;
@@ -68,7 +68,7 @@ function refFor(asset: TextureAsset, frame: TextureFrame | null): TextureRef | n
   if (!isTextureFile(asset.file)) return null;
   return {
     file: asset.file,
-    smooth: String(asset.props.filter ?? 'linear') !== 'nearest',
+    smooth: textOf(asset.props.filter ?? 'linear') !== 'nearest',
     rect: frame ? { x: frame.x, y: frame.y, w: frame.w, h: frame.h } : null,
     sourceWidth: asset.width,
     sourceHeight: asset.height,