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/tests/test_routes_games.py

@@ -39,9 +39,19 @@ class GamesRouteTest(unittest.TestCase):
             self.assertEqual(200, snapshot.status_code)
             self.assertEqual("alice", snapshot.json()["players"][0]["sub"])
 
+            # A logged-in non-player is a read-only spectator: no join
+            # code, and the view is marked as a spectator view.
             with oidc_user("mallory"):
-                forbidden = await client.get(f"/api/games/{game_id}")
-            self.assertEqual(403, forbidden.status_code)
+                watched = await client.get(f"/api/games/{game_id}")
+            self.assertEqual(200, watched.status_code)
+            self.assertTrue(watched.json()["spectator"])
+            self.assertNotIn("join_code", watched.json())
+
+            # Anonymous users may watch too.
+            anonymous = await client.get(f"/api/games/{game_id}")
+            self.assertEqual(200, anonymous.status_code)
+            self.assertTrue(anonymous.json()["spectator"])
+            self.assertNotIn("join_code", anonymous.json())
 
     @async_test
     async def test_join_fills_seats_and_starts_game(self) -> None:
@@ -61,6 +71,7 @@ class GamesRouteTest(unittest.TestCase):
                 started = await client.post("/api/games/join", json={"code": code})
             self.assertEqual(200, started.status_code)
             state = started.json()
+            game_id = state["id"]
             self.assertEqual("playing", state["phase"])
             self.assertEqual(4, len(state["players"]))
             self.assertEqual([], state["table"])
@@ -72,6 +83,21 @@ class GamesRouteTest(unittest.TestCase):
             self.assertNotIn("hand", state["players"][0])
             self.assertEqual(1, state["turn"])
 
+            # A spectator sees the table, the score and each player's
+            # captured count and scope — but no hand at all.
+            watched = await client.get(f"/api/games/{game_id}")
+            self.assertEqual(200, watched.status_code)
+            spect = watched.json()
+            self.assertTrue(spect["spectator"])
+            self.assertNotIn("join_code", spect)
+            self.assertEqual([], spect["table"])
+            self.assertEqual({"A": 0, "B": 0}, spect["scores"])
+            for participant in spect["players"]:
+                self.assertNotIn("hand", participant)
+                self.assertEqual(10, participant["cards_left"])
+                self.assertEqual(0, participant["captured_count"])
+                self.assertEqual(0, participant["scope"])
+
     @async_test
     async def test_create_napola_option(self) -> None:
         transport = ASGITransport(app=app)