Add standalone backup script and admin update-check banner

ops/backup.sh snapshots Redis (BGSAVE, dynamic RDB path lookup) and
./config for standalone deployments, with retention. A background
service polls GitHub releases every 24h and surfaces an admin-only
banner in the UI when a newer version is published.

nodejs/utils/update_check.js

@@ -0,0 +1,66 @@
+'use strict';
+
+// Periodic "is a newer release available" check against GitHub releases.
+// Nothing auto-updates -- this only surfaces a notice (an admin-only banner,
+// see routes/update_check.js + views/top.ejs) so operators know to
+// `git pull` + rebuild on their own schedule. State lives in memory only
+// (single-process app); a restart just re-checks on the next interval.
+
+const { buildVersion } = require('./build_info');
+
+const REPO = 'theta42/proxy';
+const API_URL = `https://api.github.com/repos/${REPO}/releases/latest`;
+
+let state = {
+	currentVersion: buildVersion,
+	latestVersion: null,
+	updateAvailable: false,
+	releaseUrl: null,
+	checkedAt: null,
+	error: null,
+};
+
+// Basic semver compare (major.minor.patch, ignoring any -prerelease/+build
+// suffix) -- good enough for comparing release tags like "v1.2.0" against
+// package.json's "1.1.0". Returns true if `a` is strictly newer than `b`.
+function isNewer(a, b) {
+	const pa = a.replace(/^v/i, '').split('.').map(n => parseInt(n, 10) || 0);
+	const pb = b.replace(/^v/i, '').split('.').map(n => parseInt(n, 10) || 0);
+	for (let i = 0; i < Math.max(pa.length, pb.length); i++) {
+		const na = pa[i] || 0, nb = pb[i] || 0;
+		if (na !== nb) return na > nb;
+	}
+	return false;
+}
+
+async function checkNow() {
+	try {
+		const res = await fetch(API_URL, {
+			headers: { 'Accept': 'application/vnd.github+json', 'User-Agent': 'theta42-proxy-update-check' },
+		});
+		if (!res.ok) throw new Error(`GitHub API returned ${res.status}`);
+		const data = await res.json();
+		const latestVersion = String(data.tag_name || '').replace(/^v/i, '');
+
+		state = {
+			currentVersion: buildVersion,
+			latestVersion: latestVersion || null,
+			updateAvailable: latestVersion ? isNewer(latestVersion, buildVersion) : false,
+			releaseUrl: data.html_url || `https://github.com/${REPO}/releases/latest`,
+			checkedAt: Date.now(),
+			error: null,
+		};
+	} catch (error) {
+		// Network hiccup, rate limit, no releases published yet, etc. -- keep
+		// the previous state and just note the failure; never throw, this
+		// runs unattended on a timer.
+		state = { ...state, checkedAt: Date.now(), error: error.message };
+	}
+	return state;
+}
+
+function getState() {
+	return state;
+}
+
+module.exports = { checkNow, getState, isNewer, REPO };