Dashboard Studio 1.6.1: show version, load fresh files after updates

- Version shown under About in the dashboard settings, with a link to
  the repository; /api/version reports it
- index.html is never cached and stamps the version on every asset URL,
  so browsers can't keep running old files after an update
- Open screens check the version after reconnecting and every 5 minutes
  and reload into the new version (editing only shows a message);
  pending saves are flushed first

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

dashboard_studio/web/index.html

@@ -5,6 +5,7 @@
   <meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover">
   <meta name="theme-color" content="#f2f2f7" media="(prefers-color-scheme: light)">
   <meta name="theme-color" content="#0f0f11" media="(prefers-color-scheme: dark)">
+  <meta name="ds-version" content="__VERSION__">
   <title>Dashboard Studio</title>
   <link rel="icon" type="image/png" href="static/favicon.png">
   <link rel="stylesheet" href="static/style.css">