feat(txt-game): initial module scaffold

Number guessing game (1-100, 7 attempts) as a HAL custom-app module.
Serves HTML form UI with per-session state via cookie, no npm deps.
Traefik labels for txt.${DOMAIN} on websecure with letsencrypt TLS.

docker-compose.yml

@@ -0,0 +1,19 @@
+services:
+  txt-game:
+    build: .
+    restart: unless-stopped
+    environment:
+      - DOMAIN=${DOMAIN:-localhost}
+    labels:
+      - "traefik.enable=true"
+      - "traefik.http.routers.txt-game.rule=Host(`txt.${DOMAIN:-localhost}`)"
+      - "traefik.http.routers.txt-game.entrypoints=websecure"
+      - "traefik.http.routers.txt-game.tls.certresolver=letsencrypt"
+      - "traefik.http.services.txt-game.loadbalancer.server.port=3000"
+    networks:
+      - proxy
+      - default
+
+networks:
+  proxy:
+    external: true