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

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Summary

Introduces a long-lived pid cookie (365 d, HttpOnly, SameSite=Strict) for persistent player identity alongside the existing 24 h sid session cookie
On first visit, player row is upserted into players (idempotent). On round end, a transaction inserts into games and updates aggregates: best_attempts (wins only), streaks, last_played_at
DB failures are caught, logged, and swallowed — the game keeps serving (degraded mode when env vars are missing)
Adds “Your best” stats panel (played / won / lost / best attempts / streak / best streak)
Adds public top-10 scoreboard ordered by fewest best_attempts ASC, tie-broken by earliest last_played_at; identifiers truncated to 8 chars; current player row highlighted

Added package.json (pg ^8.13.3, "type":"module") and committed package-lock.json
Dockerfile now copies package.json + lockfile and runs npm ci --omit=dev before copying server.mjs
docker-compose.yml forwards all provisioned TXT_GAME_DB_* env vars into the container and joins the postgres_postgres network for container-to-container postgres access
module.yml version unchanged (builder owns versioning)

Pipeline builds successfully (check after merge)
https://txt.zurag.be serves the updated UI with stats panel + scoreboard sections
Play a winning game → “Your best” shows attempts; scoreboard shows row with 8-char truncated ID
Play a losing game → games_lost increments, streak resets to 0
Restart container via HAL docker_restart on ace → reload same incognito window → values unchanged (DB persistence verified)

Task: d1c49d59-57bd-4eba-9e22-f25a04157ad4 Blocked by (completed): 3dab55e3-9792-47a0-a4a6-ba7757517314 (schema + provisioning)