Add briscola: classic two-player and briscola a quattro

New tavolo-briscola distribution implementing briscola on the platform:

- pure rules (state.py, engine.py): 3-card deals, a face-up trump that
  is the last card drawn, trump-first trick resolution (A > 3 > K > H >
  J > 7 > 6 > 5 > 4 > 2), 120 points per deal, 60-60 patta re-deals, a
  configurable target score (default 61), deal-end acknowledgements and
  turn auto-play;
- BriscolaEngine (briscola, 2 players) and BriscolaQuattroEngine
  (briscola_a_quattro, 4 players in fixed partnerships) adapters;
- registered in tavolo-app, packaged in the Docker image, documented.

Platform fixes surfaced by a two-player lobby:

- the websocket state and snapshot payloads now carry seats_open (they
  were only in the REST lobby payload), so lobbies with player counts
  other than four render correctly; seats_open is clamped at zero;
- the web client logs unparseable server messages instead of silently
  dropping them.

Web client: briscola table for both variants (stock, face-up trump,
trick, last-trick banner), deal summary modal and game-over overlay.

Tests: tavolo-briscola rules/adapter suites, app integration tests
(lobby, websocket play, turn timeout, deal-end acks, persistence), a
platform seats_open test and frontend model parsing tests.

server/packages/tavolo-app/pyproject.toml

@@ -5,12 +5,13 @@ build-backend = "setuptools.build_meta"
 [project]
 name = "tavolo-app"
 version = "0.1.0"
-description = "Tavolo multiplayer card-game application: platform + scopone game wiring"
+description = "Tavolo multiplayer card-game application: platform + games wiring"
 readme = "README.md"
 requires-python = ">=3.10"
 dependencies = [
     "tavolo-platform",
     "tavolo-scopone",
+    "tavolo-briscola",
     "kaya-core",
     "kaya-cors",
     "kaya-session",