feat(scores): persist scores in Postgres, add scoreboard UI

Introduces a long-lived `pid` cookie (365 d) as persistent player identity
alongside the existing 24 h `sid` session cookie.

On first visit, a player row is upserted into `players`. On round end, a
transaction inserts into `games` and updates aggregates (best_attempts on wins
only, streak counters, last_played_at). DB failures are caught and logged —
the game keeps serving.

Adds a 3×2 'Your best' stats panel and a public top-10 scoreboard (fewest
best_attempts ASC, earliest last_played_at as tie-breaker; identifiers
truncated to 8 chars; current player highlighted).

Infrastructure: adds `pg` dependency, Dockerfile now installs npm deps before
copying server.mjs, docker-compose forwards all provisioned TXT_GAME_DB_*
vars and joins the postgres_postgres network for container-to-container reach.

Task: d1c49d59-57bd-4eba-9e22-f25a04157ad4

docker-compose.yml

@@ -5,6 +5,11 @@ services:
     restart: unless-stopped
     environment:
       - DOMAIN=${DOMAIN:-localhost}
+      - TXT_GAME_DB_HOST=${TXT_GAME_DB_HOST}
+      - TXT_GAME_DB_PORT=${TXT_GAME_DB_PORT}
+      - TXT_GAME_DB_USER=${TXT_GAME_DB_USER}
+      - TXT_GAME_DB_PASSWORD=${TXT_GAME_DB_PASSWORD}
+      - TXT_GAME_DB_NAME=${TXT_GAME_DB_NAME}
     labels:
       - "traefik.enable=true"
       - "traefik.http.routers.txt-game.rule=Host(`txt.${DOMAIN:-localhost}`)"
@@ -13,7 +18,10 @@ services:
       - "traefik.http.services.txt-game.loadbalancer.server.port=3000"
     networks:
       - proxy
+      - postgres_postgres
 
 networks:
   proxy:
     external: true
+  postgres_postgres:
+    external: true