security: use crypto.randomUUID for temp file suffix (SonarCloud S2245)

Replace Math.random() with crypto.randomUUID() when generating the unique
suffix for the atomic write-then-move temp file. The value isn't security-
sensitive, but a CSPRNG gives a stronger uniqueness guarantee and resolves
SonarCloud javascript:S2245.

apps/effectcraft-web/js/host.js

@@ -495,7 +495,7 @@ export async function cacheRead(name) {
 export async function cacheWrite(fullName, bytes) {
   const [dir, name] = await entryDir(fullName);
   const canMove = typeof FileSystemHandle !== "undefined" && "move" in FileSystemHandle.prototype;
-  const tmp = canMove ? `${name}.tmp.${Math.random().toString(36).slice(2)}` : name;
+  const tmp = canMove ? `${name}.tmp.${crypto.randomUUID()}` : name;
   const fh = await dir.getFileHandle(tmp, { create: true });
   if (fh.createSyncAccessHandle) {
     const h = await fh.createSyncAccessHandle();