feat: route wallet traffic through the Temetro Network relay (v0.7.0)

Devices no longer connect to the backend directly. The /wallet Socket.io
namespace is removed from realtime.ts; a new services/relay-client.ts connects
to the standalone Temetro Network relay's /hub namespace (RELAY_TOKEN-auth),
emitToWallet delegates to its sendToWallet, and device responses + wallet:online
replay are handled there via the same wallet-share/wallet-updates services.

- Add RELAY_URL + RELAY_TOKEN env (env.ts, .env.example, docker-compose.yml);
  the wallet-import QR (resolveRelayUrl) now points at RELAY_URL.
- Add socket.io-client dependency.
- Document the Temetro Network folder/service in root + backend CLAUDE.md.
- Bump root/backend/frontend to 0.7.0; CHANGELOG entry.

The relay service itself lives in github.com/temetro/temetro-network.

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

backend/src/routes/patients-wallet.ts

@@ -27,9 +27,12 @@ export const patientsWalletRouter = Router();
 patientsWalletRouter.use(requireAuth, requireOrg);
 
 // The device-reachable URL the patient's app should connect to (baked into the
-// QR). Prefer an explicit PUBLIC_RELAY_URL; otherwise derive it from the request
-// host so that opening the web app over the LAN yields a reachable LAN URL.
+// QR). Devices connect to the standalone Temetro Network relay — the same relay
+// this backend is hubbed to — so RELAY_URL is the canonical answer. The legacy
+// PUBLIC_RELAY_URL / cloudflared / request-host fallbacks remain for pre-relay
+// self-hosting.
 async function resolveRelayUrl(req: Request): Promise<string> {
+  if (env.RELAY_URL) return env.RELAY_URL;
   if (env.PUBLIC_RELAY_URL) return env.PUBLIC_RELAY_URL;
   // A cloudflared quick tunnel (`npm run docker:tunnel`). Wait briefly for it to
   // become reachable so the QR never carries a not-yet-live URL.