release: 3.40.2 — file-filter reset (✕) button

A red ✕ next to the filter selector appears whenever the filter is not
"All" and resets it to "All" in one click (pysimFsFilterClear).  Bump
VERSION/pyproject/PWA header to 3.40.2 and the SW cache to simple-v487.

frontend/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'simple-v486';
+const CACHE = 'simple-v487';
 const URLS = [
   'index.html',
   'help.html',