backend: version + network endpoints, LAN-friendly CORS/origins

Add public GET /api/version (current version + GitHub-release update check,
cached, fail-soft) and GET /api/network (detected LAN addresses). Accept
localhost/private-LAN origins in CORS and Better Auth trusted origins via a
shared isAllowedOrigin helper, so staff can reach the app over the clinic
network. The seed-demo.ts fake test data is removed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/src/routes/version.ts

@@ -0,0 +1,76 @@
+// GET /api/version — reports the running version and whether a newer release
+// exists on GitHub. Public (no PHI); the frontend uses it for the Settings
+// "About & Updates" panel and the optional update banner.
+import { createRequire } from "node:module";
+
+import { Router } from "express";
+
+import { env } from "../env.js";
+
+const require = createRequire(import.meta.url);
+// package.json is the source of truth for the running version (copied into the
+// runtime image). APP_VERSION can override it (set by the release pipeline).
+const pkg = require("../../package.json") as { version?: string };
+const CURRENT = env.APP_VERSION ?? pkg.version ?? "0.0.0";
+
+const LATEST_RELEASE_URL =
+  "https://api.github.com/repos/temetro/temetro/releases/latest";
+const CACHE_TTL = 6 * 60 * 60 * 1000; // 6h — releases are infrequent.
+const ERROR_TTL = 10 * 60 * 1000; // back off ~10m after a failed lookup.
+
+type LatestInfo = { latest: string | null; releaseUrl: string | null };
+let cache: { at: number; ttl: number; info: LatestInfo } | null = null;
+
+function parseSemver(v: string): [number, number, number] | null {
+  const m = v.trim().replace(/^v/, "").match(/^(\d+)\.(\d+)\.(\d+)/);
+  return m ? [Number(m[1]), Number(m[2]), Number(m[3])] : null;
+}
+
+/** True if `latest` is a strictly newer semver than `current`. */
+function isNewer(latest: string, current: string): boolean {
+  const a = parseSemver(latest);
+  const b = parseSemver(current);
+  if (!a || !b) return false;
+  for (let i = 0; i < 3; i++) {
+    if (a[i]! > b[i]!) return true;
+    if (a[i]! < b[i]!) return false;
+  }
+  return false;
+}
+
+async function fetchLatest(): Promise<LatestInfo> {
+  if (cache && Date.now() - cache.at < cache.ttl) return cache.info;
+  try {
+    const res = await fetch(LATEST_RELEASE_URL, {
+      headers: { Accept: "application/vnd.github+json", "User-Agent": "temetro" },
+      signal: AbortSignal.timeout(5000),
+    });
+    if (!res.ok) throw new Error(`GitHub responded ${res.status}`);
+    const body = (await res.json()) as { tag_name?: string; html_url?: string };
+    const info: LatestInfo = {
+      latest: body.tag_name ? body.tag_name.replace(/^v/, "") : null,
+      releaseUrl: body.html_url ?? null,
+    };
+    cache = { at: Date.now(), ttl: CACHE_TTL, info };
+    return info;
+  } catch {
+    // Fail soft: keep any prior value, briefly cache the miss to avoid hammering.
+    const info: LatestInfo = cache?.info ?? { latest: null, releaseUrl: null };
+    cache = { at: Date.now(), ttl: ERROR_TTL, info };
+    return info;
+  }
+}
+
+const router = Router();
+
+router.get("/", async (_req, res) => {
+  const { latest, releaseUrl } = await fetchLatest();
+  res.json({
+    current: CURRENT,
+    latest,
+    updateAvailable: latest ? isNewer(latest, CURRENT) : false,
+    releaseUrl,
+  });
+});
+
+export const versionRouter = router;