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/requirements.txt

@@ -4,10 +4,11 @@
 #
 #    pip-compile --allow-unsafe --extra otel --extra-index-url=https://pypi.org/simple --index-url=https://gitea.woggioni.net/api/packages/woggioni/pypi/simple --output-file=../../requirements.txt pyproject.toml
 #
-# NOTE: the tavolo-platform, tavolo-scopone and tavolo-app sibling packages
-# are NOT pinned here: they are installed from ./packages in the Dockerfile
-# and in development (pip install -e ./packages/tavolo-platform
-# -e ./packages/tavolo-scopone -e ./packages/tavolo-app). All of their
+# NOTE: the tavolo-platform, tavolo-scopone, tavolo-briscola and tavolo-app
+# sibling packages are NOT pinned here: they are installed from ./packages in
+# the Dockerfile and in development (pip install -e ./packages/tavolo-platform
+# -e ./packages/tavolo-scopone -e ./packages/tavolo-briscola
+# -e ./packages/tavolo-app). All of their
 # third-party dependencies are direct dependencies of tavolo-app, so this
 # lock covers the full closure. The otel extra (kaya-otel and its
 # OpenTelemetry dependencies) IS included, so OTEL_ENABLED works in the