feat(terminal): proxy /terminal (+WebSocket) through the Void app to ttyd

Makes the embedded Terminal work via the raw LAN IP too (bypasses Traefik's
/terminal route). ttyd base-path preserved; firewall on CT300 opened to the app host.

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

package.json

@@ -16,6 +16,7 @@
     "dompurify": "^3.4.7",
     "dotenv": "^17.4.2",
     "express": "^5.2.1",
+    "http-proxy": "^1.18.1",
     "jsdom": "^29.1.1",
     "marked": "^18.0.4",
     "multer": "^2.1.1",