add(ui/ux): show the running version and build stamp in the header

static/app.js

@@ -1619,9 +1619,21 @@ function onLangChange() {
   if (scanItems.length) renderImportTable();
 }
 
+// ---- version ----
+// the build stamp is the quickest answer to "did the redeploy arrive?"
+async function showVersion() {
+  try {
+    const v = await api("/api/version");
+    // the version alone rarely moves, so the stamp is what tells deploys apart
+    $("#app-version").textContent = `v${v.version} · ${v.build || v.built_at}`;
+    $("#app-version").title = `${v.built_at} UTC${v.build ? " · " + v.build : ""}`;
+  } catch {}
+}
+
 // ---- init ----
 applyI18n();
 updateLangButton();
 endLibraryEdit();
 loadLibraries();
 refreshMissingBadge();
+showVersion();