perf: keep heavy work off UI thread

scripts/build-web-worker.sh

@@ -0,0 +1,10 @@
+#!/bin/sh
+set -eu
+
+cargo build --release --target wasm32-unknown-unknown --package ocs_web_worker
+mkdir -p web/worker_pkg
+wasm-bindgen \
+  --target web \
+  --out-dir web/worker_pkg \
+  --out-name ocs_web_worker \
+  target/wasm32-unknown-unknown/release/ocs_web_worker.wasm