Bundled Roundcube webmail in the Mail tab, optional Microsoft 365 OAuth sign-in, collapsible menu

- docker-compose: roundcube service with inline config (Gmail/iCloud/Yahoo presets, framing allowed, persistent key); only reachable through the hub
- hub passes /webmail/ through to Roundcube behind the passkey sign-in; Microsoft's sign-in page opens in the whole window and returns to the Mail tab
- M365_* settings add 'Login with Microsoft 365' (README has the Entra app registration steps)
- Side menu collapses to icons or hides completely (remembered per device, Ctrl/Cmd+B)
- tools/webmail-test.js

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

public/sw.js

@@ -12,7 +12,7 @@ self.addEventListener('activate', e => {
 });
 self.addEventListener('fetch', e => {
   const u = new URL(e.request.url);
-  if (e.request.method !== 'GET' || u.origin !== location.origin || u.pathname.startsWith('/sf/') || u.pathname.startsWith('/plex/') || u.pathname.startsWith('/api/')) return;
+  if (e.request.method !== 'GET' || u.origin !== location.origin || u.pathname.startsWith('/sf/') || u.pathname.startsWith('/plex/') || u.pathname.startsWith('/webmail') || u.pathname.startsWith('/api/')) return;
   e.respondWith(fetch(e.request).then(r => {
     if (r.ok) { const copy = r.clone(); caches.open(CACHE).then(c => c.put(e.request, copy)); }
     return r;