release: 3.40.0 — file-tree filter

Bump VERSION/pyproject/PWA header to 3.40.0 and the SW cache to
simple-v485 (index.html changed).  CHANGELOG [3.40.0] documents the
file-tree filter (checkbox multiselect, path-exact DF hiding, expand/
collapse all, auto-expand, and the "To EF filter" cross-link).

frontend/index.html

@@ -1989,7 +1989,7 @@
 // ===== Version =====
 // Single source of truth for the PWA version: shown in the header and used
 // by the server version check in pysimConnect().
-const SIMPLE_VERSION = '3.39.0';
+const SIMPLE_VERSION = '3.40.0';
 document.getElementById('app-version').textContent = 'v' + SIMPLE_VERSION;
 
 // ===== view history (the browser Back/Forward buttons) =====

frontend/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'simple-v484';
+const CACHE = 'simple-v485';
 const URLS = [
   'index.html',
   'help.html',