A game that stays silent is only half a game, so a sound is an asset like any other (#45)

Sounds follow the road fonts already paved: the file goes to the server
content-addressed under its sha256, the project keeps a named asset that
points at it, and nothing is ever re-encoded. The format is read from the
file's own signature, not from what the browser claims - the same .m4a
arrives as audio/mp4, audio/x-m4a or as nothing at all.

Playing is two nodes. "Play sound" takes the asset and may raise or lower
its volume; every call is its own voice, so two jumps in a row are two
jumps heard. Its loop input is a choice of three - from the asset, on,
off - because a checkbox has to spend one of its two positions on "not
set" and would lose a case: an asset that loops could then never be
played once.

Below the graph core stays browser-free: NodeContext hands out an asset
id, BehaviorSystem resolves it against the project and folds the asset's
own volume and loop into the call, and only viewport/SoundLibrary knows
about Web Audio. A run without a sink plays nothing instead of throwing.

The CI browser is muted, so the ear is no witness: the debug hook counts
started and stopped voices, and step 34 reads that counter.

src/core/store/serialize.ts

@@ -17,6 +17,7 @@ import { isShaderNodeDef } from '../shader/nodes';
 import type { Asset, StateMachineAsset, TextureFrame } from '../model/Asset';
 import { isAssetType } from '../model/AssetTypes';
 import { isFontFile } from '../model/font';
+import { isSoundFile } from '../model/sound';
 import { emptyEdit, type InstanceEdit, isEmptyEdit } from '../model/instance';
 import {
   type FieldValue,
@@ -153,6 +154,9 @@ export function deserializeProject(raw: unknown, fallbackId = ''): Project {
     } else if (type === 'font') {
       const file = typeof a.file === 'string' && isFontFile(a.file) ? a.file : '';
       assets.push({ id, type, name, props, file });
+    } else if (type === 'sound') {
+      const file = typeof a.file === 'string' && isSoundFile(a.file) ? a.file : '';
+      assets.push({ id, type, name, props, file });
     } else if (type === 'animation') {
       // Kept even when they dangle, like a sprite's `texture`: a frame reads as no picture.
       const frames = Array.isArray(a.frames) ? a.frames : [];