Set scopa targets to their traditional defaults

Partnership games go to 21: scopone scientifico (the tournament target)
and scopa a quattro, while two-player scopa keeps its usual 11. The scopa
package resolves the default from the player count and exposes a per
variant options_schema default, so the lobby creation form shows the
right value without frontend changes.

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

@@ -172,11 +172,20 @@ class DealTest(unittest.TestCase):
     def test_create_game_defaults(self) -> None:
         state = engine.create_game("p0", "p0")
         self.assertEqual(2, state.player_count)
+        # Two-player scopa is traditionally played to 11 points.
         self.assertEqual(11, state.target_score)
         self.assertFalse(state.asso_pigliatutto)
         self.assertEqual("p0", state.players[0].sub)
         self.assertEqual("lobby", state.phase)
 
+    def test_create_game_four_player_default_target(self) -> None:
+        # The four-player partnership game (like scopone) goes to 21.
+        state = engine.create_game("p0", "p0", player_count=4)
+        self.assertEqual(21, state.target_score)
+        # An explicit target still wins over the default.
+        explicit = engine.create_game("p0", "p0", player_count=4, target_score=16)
+        self.assertEqual(16, explicit.target_score)
+
     def test_create_game_player_count_validation(self) -> None:
         for bad in (1, 3, 5, 0):
             with self.assertRaises(IllegalMove):