feat: show app version and server build tag in settings

Adds an About section at the bottom of Settings displaying the app
version. In WEB mode it fetches /api/version and appends the live
server build tag so you can confirm which deploy is running.

frontend/app.js

@@ -1550,6 +1550,19 @@ async function renderSettings() {
           <button id="resetAppBtn" class="btn danger">Reset app</button>
         </div>
       </div>
+    </div>
+
+    <div class="set-group">
+      <div class="set-group-title">About</div>
+      <div class="set-row">
+        <span>
+          Version
+          <small>App version and current build.</small>
+        </span>
+        <div class="set-actions" style="margin:0">
+          <span id="aboutVersion" class="about-version">v${APP_VERSION}</span>
+        </div>
+      </div>
     </div>`;
 
   c.appendChild(wrap);
@@ -1656,6 +1669,18 @@ async function renderSettings() {
   $('importBackupBtn').addEventListener('click', () => $('backupFileInput').click());
   $('backupFileInput').addEventListener('change', importBackup);
 
+  // ---- About: append server build tag (WEB mode only) ----
+  if (WEB) {
+    try {
+      const res = await fetch('/api/version', { cache: 'no-store' });
+      if (res.ok && view.type === 'settings') {
+        const v = await res.json();
+        const el = $('aboutVersion');
+        if (el && v.buildTag) el.textContent = `v${v.version || APP_VERSION} · build ${v.buildTag}`;
+      }
+    } catch { /* offline — leave the static version in place */ }
+  }
+
   // ---- Reset ----
   $('refreshUiBtn').addEventListener('click', async () => {
     const btn = $('refreshUiBtn');