Add a Check for updates button under Settings; keep the self edge when settings are saved

Saving settings replaced the whole Settings value, which would have dropped SelfEdgeID and made the
next start create a second self edge with a new token.

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

web/index.html

@@ -925,12 +925,24 @@ serverViews.settings = async () => {
   const staging = chk('Use the Let\'s Encrypt staging server (untrusted test certificates)', s.acmeStaging);
   const save = act(async () => { await api('PUT', '/api/admin/settings', {dashboardUrl:f.url.value, acmeEmail:f.acme.value, acmeStaging:staging.box.checked,
     smtp:{host:f.host.value, port:+f.port.value, user:f.user.value, pass:f.pass.value, from:f.from.value, mode:f.mode.value}}); S.me = await api('GET', '/api/me'); toast('Saved'); });
+  const updOut = h('div', {class:'dim'}, 'Not checked yet.');
+  const checkUpdate = act(async () => {
+    updOut.textContent = 'Checking…';
+    const u = await api('GET', '/api/admin/update');
+    const dev = !/^v\d+\.\d+\.\d+$/.test(u.current || '');
+    if (u.error) updOut.textContent = 'Running ' + (u.current || 'an unknown version') + '. Could not check for updates: ' + u.error;
+    else if (dev) updOut.textContent = 'This is a development build (' + (u.current || 'unversioned') + '). The newest release is ' + u.latest + '.';
+    else if (u.newer) updOut.textContent = 'Running ' + u.current + '. ' + u.latest + ' is available. ' + (u.autoUpdate ? 'Auto-update is on, so it installs by itself within about six hours.' : 'Auto-update is off: install it yourself, or set HAMMERHEAD_AUTO_UPDATE=1 and restart.');
+    else updOut.textContent = 'Running ' + u.current + ', which is the newest release.';
+  });
   return h('div', {},
     card('General', h('div', {class:'stack'}, field('Dashboard URL', f.url, 'The address people use to reach Hammerhead. Used for login redirects and SSO. Include https:// if you serve it over TLS.'),
       field('Let\'s Encrypt contact email', f.acme, 'Used for certificate expiry notices'), staging)),
     card('Email', h('p', {class:'dim'}, 'Needed for invitation emails and one-time sign-in codes.'),
       h('div', {class:'grid'}, field('SMTP host', f.host), field('Port', f.port), field('Security', f.mode), field('Username', f.user), field('Password', f.pass), field('From', f.from)),
       h('div', {class:'actions', style:'margin-top:10px'}, h('button', {class:'ghost', onclick: act(async () => { await save(); await api('POST', '/api/admin/settings/test-mail'); toast('Test email sent to ' + S.me.email); })}, 'Save and send a test email'))),
+    card('Updates', h('p', {class:'dim'}, 'Hammerhead, Blacktip and Bamboo can update themselves from new releases when auto-update is on (HAMMERHEAD_AUTO_UPDATE=1). This checks the newest release for Hammerhead; it installs nothing.'),
+      updOut, h('div', {class:'actions', style:'margin-top:10px'}, h('button', {class:'ghost', onclick:checkUpdate}, 'Check for updates'))),
     h('button', {class:'btn', onclick:save}, 'Save settings'));
 };