Let anyone with the game URL watch as a read-only spectator

Anonymous users and logged-in non-players can now open /game/<id> and
follow the match: they see the table, the score and each player's
captured cards and scope, but never a hand and never the join code.
Spectator actions are rejected with a forbidden error.

Backend (tavolo-platform / tavolo-scopone):
- /ws/games/{id} accepts anonymous and non-seated connections as
  spectators; only unknown games are refused. The state payload carries
  spectator: true and withholds join_code unless the viewer is seated.
- GET /api/games/{id} is public and returns the same personalized
  (player) or read-only (spectator) view.
- GameEngine.view_for/game_over_view take Optional[str] (None = spectator)
  and are documented to hide privileged information for non-seated
  viewers.

Frontend (Sycamore):
- Parse the spectator flag and render a spectator table: card backs plus
  captured/scope for every seat, no clickable hand, "Spectating" badge.
- A pre-start spectator sees a "game not started yet" waiting room with
  the watch link and no join code.
- "Copy watch link" buttons in the waiting room and the game HUD.
- The hand-end summary carries no acknowledge button for spectators and
  the game-over overlay hides "My matches".

Tests and docs updated.

server/packages/tavolo-scopone/src/tavolo/scopone/engine.py

@@ -528,13 +528,14 @@ def hand_points(state: ScoponeState) -> Tuple[List[int], Dict[str, object]]:
     return points, details
 
 
-def state_for_player(state: ScoponeState, sub: str) -> Dict[str, object]:
+def state_for_player(state: ScoponeState, sub: Optional[str]) -> Dict[str, object]:
     """Serialize ``state`` hiding other players' hands.
 
     Hands are reduced to a count, except for the requesting player's own
-    hand. Non-seated viewers simply see no hand at all. The platform
-    merges the session envelope (``id``, ``join_code``, ``game_type``)
-    into the view itself.
+    hand. Non-seated viewers — including spectators, for whom ``sub`` is
+    ``None`` — simply see no hand at all. The platform merges the session
+    envelope (``id``, ``join_code`` for seated players, ``game_type``,
+    ``spectator``) into the view itself.
     """
     viewer = state.player_for(sub)
     players: List[Dict[str, object]] = []

server/packages/tavolo-scopone/src/tavolo/scopone/plugin.py

@@ -171,13 +171,13 @@ class ScoponeEngine(GameEngine):
         else:
             raise IllegalMove(f"unknown action: {action!r}")
 
-    def view_for(self, session: GameSession, user_sub: str) -> Dict[str, Any]:
+    def view_for(self, session: GameSession, user_sub: Optional[str]) -> Dict[str, Any]:
         return engine.state_for_player(session.state, user_sub)
 
     def is_finished(self, session: GameSession) -> bool:
         return session.state.phase == PHASE_FINISHED
 
-    def game_over_view(self, session: GameSession, user_sub: str) -> Dict[str, Any]:
+    def game_over_view(self, session: GameSession, user_sub: Optional[str]) -> Dict[str, Any]:
         state: ScoponeState = session.state
         return {
             "scores": {"A": state.scores[0], "B": state.scores[1]},

server/packages/tavolo-scopone/src/tavolo/scopone/state.py

@@ -239,7 +239,7 @@ class ScoponeState:
 
     # -- helpers ----------------------------------------------------------
 
-    def player_for(self, sub: str) -> Optional[PlayerState]:
+    def player_for(self, sub: Optional[str]) -> Optional[PlayerState]:
         for player in self.players:
             if player.sub == sub:
                 return player

server/packages/tavolo-scopone/tests/test_engine.py

@@ -574,6 +574,27 @@ class MatchFlowTest(unittest.TestCase):
         self.assertEqual(["07C"], view["table"])
         self.assertTrue(view.get("your_turn"))
 
+    def test_state_for_player_spectator_sees_public_info_only(self) -> None:
+        state = make_state(
+            [["02D", "03C"], ["04D"], ["05D"], ["06D"]],
+            table=["07C"],
+            captured=[["01D"], [], ["02C"], ["03B"]],
+            scope=[1, 0, 2, 0],
+        )
+        view = engine.state_for_player(state, None)
+        for player in view["players"]:
+            self.assertNotIn("hand", player)
+        self.assertNotIn("your_turn", view)
+        self.assertNotIn("legal_moves", view)
+        # The public table state is still fully visible.
+        self.assertEqual(["07C"], view["table"])
+        self.assertEqual({"A": 0, "B": 0}, view["scores"])
+        players = {p["seat"]: p for p in view["players"]}
+        self.assertEqual(1, players[0]["captured_count"])
+        self.assertEqual(1, players[0]["scope"])
+        self.assertEqual(2, players[2]["scope"])
+        self.assertEqual(1, players[1]["cards_left"])
+
     def test_legal_moves_only_for_player_on_turn(self) -> None:
         state = make_state([["02D", "03C"], ["04D"], ["05D"], ["06D"]],
                            table=["07C"])

server/packages/tavolo-scopone/tests/test_plugin.py

@@ -160,6 +160,17 @@ class ViewTest(unittest.TestCase):
         self.assertNotIn("join_code", view)
         self.assertNotIn("game_type", view)
 
+    def test_view_for_spectator_hides_all_hands(self) -> None:
+        engine = ScoponeEngine()
+        session = _started(engine)
+        view = engine.view_for(session, None)
+        for player in view["players"]:
+            self.assertNotIn("hand", player)
+        self.assertNotIn("your_turn", view)
+        self.assertNotIn("legal_moves", view)
+        self.assertIn("table", view)
+        self.assertEqual({"A": 0, "B": 0}, view["scores"])
+
     def test_lobby_view(self) -> None:
         engine = ScoponeEngine()
         session = _session(engine, target_score=16)