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/docker-compose.yml

@@ -68,6 +68,11 @@ services:
       BETTER_AUTH_URL: http://localhost:4000
       FRONTEND_URL: http://localhost:3000
       PORT: "4000"
+      # Temetro Network relay (github.com/temetro/temetro-network). Set RELAY_URL
+      # to your deployed relay's public URL and RELAY_TOKEN to the shared secret
+      # you configured on it — both are required for patient-wallet import.
+      RELAY_URL: ${RELAY_URL:-}
+      RELAY_TOKEN: ${RELAY_TOKEN:-}
       NODE_ENV: production
       # Uploaded patient/lab files live here, on the temetro_uploads volume.
       UPLOAD_DIR: /var/lib/temetro/uploads