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/package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "temetro-backend",
-  "version": "0.1.0",
+  "version": "0.6.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "temetro-backend",
-      "version": "0.1.0",
+      "version": "0.6.0",
       "license": "MIT",
       "dependencies": {
         "@ai-sdk/anthropic": "^3.0.84",
@@ -28,6 +28,7 @@
         "nodemailer": "^8.0.10",
         "pg": "^8.21.0",
         "socket.io": "^4.8.3",
+        "socket.io-client": "^4.8.3",
         "zod": "^4.4.3"
       },
       "devDependencies": {
@@ -3339,6 +3340,40 @@
         "node": ">=10.2.0"
       }
     },
+    "node_modules/engine.io-client": {
+      "version": "6.6.6",
+      "resolved": "https://registry.npmjs.org/engine.io-client/-/engine.io-client-6.6.6.tgz",
+      "integrity": "sha512-iY6QdftLQ9pyiPoX082bpf/u1UewnOaJrtJIF9T0++QB34lZrj0uP+Q/bj8AlUsAxqhnkTV2BS8SBZSxOmoV5Q==",
+      "license": "MIT",
+      "dependencies": {
+        "@socket.io/component-emitter": "~3.1.0",
+        "debug": "~4.4.1",
+        "engine.io-parser": "~5.2.1",
+        "ws": "~8.21.0",
+        "xmlhttprequest-ssl": "~2.1.1"
+      }
+    },
+    "node_modules/engine.io-client/node_modules/ws": {
+      "version": "8.21.0",
+      "resolved": "https://registry.npmjs.org/ws/-/ws-8.21.0.tgz",
+      "integrity": "sha512-Vsp28b7DRcimFQvrqu2Wek3z1iYxDCWqHYB8Qsnk/S4RfaCQzPGPyBNuVjJV3cd6UiKtUtp6sNM77gWvzcCH+g==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=10.0.0"
+      },
+      "peerDependencies": {
+        "bufferutil": "^4.0.1",
+        "utf-8-validate": ">=5.0.2"
+      },
+      "peerDependenciesMeta": {
+        "bufferutil": {
+          "optional": true
+        },
+        "utf-8-validate": {
+          "optional": true
+        }
+      }
+    },
     "node_modules/engine.io-parser": {
       "version": "5.2.3",
       "resolved": "https://registry.npmjs.org/engine.io-parser/-/engine.io-parser-5.2.3.tgz",
@@ -4947,6 +4982,21 @@
         "ws": "~8.20.1"
       }
     },
+    "node_modules/socket.io-client": {
+      "version": "4.8.3",
+      "resolved": "https://registry.npmjs.org/socket.io-client/-/socket.io-client-4.8.3.tgz",
+      "integrity": "sha512-uP0bpjWrjQmUt5DTHq9RuoCBdFJF10cdX9X+a368j/Ft0wmaVgxlrjvK3kjvgCODOMMOz9lcaRzxmso0bTWZ/g==",
+      "license": "MIT",
+      "dependencies": {
+        "@socket.io/component-emitter": "~3.1.0",
+        "debug": "~4.4.1",
+        "engine.io-client": "~6.6.1",
+        "socket.io-parser": "~4.2.4"
+      },
+      "engines": {
+        "node": ">=10.0.0"
+      }
+    },
     "node_modules/socket.io-parser": {
       "version": "4.2.6",
       "resolved": "https://registry.npmjs.org/socket.io-parser/-/socket.io-parser-4.2.6.tgz",
@@ -5779,6 +5829,14 @@
         "url": "https://github.com/sponsors/sindresorhus"
       }
     },
+    "node_modules/xmlhttprequest-ssl": {
+      "version": "2.1.2",
+      "resolved": "https://registry.npmjs.org/xmlhttprequest-ssl/-/xmlhttprequest-ssl-2.1.2.tgz",
+      "integrity": "sha512-TEU+nJVUUnA4CYJFLvK5X9AOeH4KvDvhIfm0vV1GaQRtchnG0hgK5p8hw/xjv8cunWYCsiPCSDzObPyhEwq3KQ==",
+      "engines": {
+        "node": ">=0.4.0"
+      }
+    },
     "node_modules/xtend": {
       "version": "4.0.2",
       "resolved": "https://registry.npmjs.org/xtend/-/xtend-4.0.2.tgz",