Add hand-end scoring summary screen with acknowledgement

After each hand of an unfinished match the game now pauses in a new
hand_end phase instead of dealing immediately:

- engine: hand_points gains an 'award' map (which team won each category),
  _end_hand stops at hand_end with a deadline, new acknowledge_hand deals
  the next hand once all four players have acked; plays are rejected while
  the summary is up
- state: acked seats, hand_end_deadline and hand_ack_timeout are persisted
  and exposed in the personalized view (also on the finished state, so the
  final hand is explained before the result)
- ws: new {"action": "ack"}; a per-hand timer force-deals the next hand
  after HAND_ACK_TIMEOUT_SECONDS (new env var, default 30s) so an away
  player cannot stall the match
- web: modal explaining each category in plain language with icons (card
  images for denara/settebello/primiera), team-coloured rows, running
  totals with progress bars, an 'Understood — next hand' button that turns
  into 'Waiting for …' plus an auto-continue countdown; the final screen
  shows the last hand's breakdown too

Verified in the browser against the compose stack: hand played to
completion, summary rendered (including a carte tie), ack from all four
players dealt the next hand live, and the auto-continue path fired when
nobody acked. 60 backend tests + mypy + cargo tests green.

server/tests/test_engine.py

@@ -297,6 +297,10 @@ class MatchFlowTest(unittest.TestCase):
 
         moves = 0
         while state.phase != PHASE_FINISHED and moves < 200000:
+            if state.phase == "hand_end":
+                for p in state.players:
+                    engine.acknowledge_hand(state, p.sub)
+                continue
             player = next(p for p in state.players if p.seat == state.turn)
             played = player.hand[0]
             options = engine.legal_captures(state.table, played)
@@ -313,5 +317,78 @@ class MatchFlowTest(unittest.TestCase):
         self.assertTrue(state.finished_at)
 
 
+class HandEndAckTest(unittest.TestCase):
+    def _hand_end_state(self) -> GameState:
+        """Drive a game into the hand_end phase with a one-card hand."""
+        state = make_state([["02D"], [], [], []],
+                           table=["02C"], target=11)
+        engine.play(state, "p0", "02D", ["02C"])
+        return state
+
+    def test_end_of_hand_pauses_for_acknowledgement(self) -> None:
+        state = self._hand_end_state()
+        self.assertEqual("hand_end", state.phase)
+        # Nobody has acknowledged yet, and no new hand was dealt.
+        self.assertEqual([], state.acked)
+        self.assertEqual(1, state.hand_number)
+        self.assertTrue(state.hand_end_deadline)
+        # Capture piles stay visible during the summary.
+        self.assertEqual(["02C", "02D"],
+                         [c.code for c in state.players[0].captured])
+        # The summary carries the award map.
+        summary = state.hand_scores[-1]
+        self.assertEqual(1, summary["hand"])
+        self.assertIn("award", summary)
+
+    def test_play_during_hand_end_is_rejected(self) -> None:
+        state = self._hand_end_state()
+        with self.assertRaises(IllegalMove):
+            engine.play(state, "p0", "02D")
+
+    def test_ack_all_four_deals_next_hand(self) -> None:
+        state = self._hand_end_state()
+        dealer_before = state.dealer
+        for i, sub in enumerate(("p0", "p1", "p2")):
+            engine.acknowledge_hand(state, sub)
+            self.assertEqual(list(range(i + 1)), state.acked)
+            self.assertEqual("hand_end", state.phase)
+        engine.acknowledge_hand(state, "p3")
+        self.assertEqual("playing", state.phase)
+        self.assertEqual(2, state.hand_number)
+        self.assertEqual((dealer_before + 1) % 4, state.dealer)
+        self.assertEqual([], state.acked)
+        self.assertIsNone(state.hand_end_deadline)
+        self.assertIsNone(state.last_move)
+        for player in state.players:
+            self.assertEqual(10, len(player.hand))
+            self.assertEqual([], player.captured)
+        self.assertEqual((dealer_before + 2) % 4, state.turn)
+
+    def test_double_ack_is_idempotent(self) -> None:
+        state = self._hand_end_state()
+        engine.acknowledge_hand(state, "p0")
+        engine.acknowledge_hand(state, "p0")
+        self.assertEqual([0], state.acked)
+
+    def test_ack_outside_hand_end_is_rejected(self) -> None:
+        state = make_state([["02D"], ["03D"], ["04D"], ["05D"]], table=[])
+        with self.assertRaises(IllegalMove):
+            engine.acknowledge_hand(state, "p0")
+
+    def test_ack_by_non_player_is_rejected(self) -> None:
+        state = self._hand_end_state()
+        with self.assertRaises(NotYourTurn):
+            engine.acknowledge_hand(state, "mallory")
+
+    def test_state_exposes_ack_progress(self) -> None:
+        state = self._hand_end_state()
+        engine.acknowledge_hand(state, "p1")
+        view = engine.state_for_player(state, "p0")
+        self.assertEqual([1], view["acknowledged"])
+        self.assertTrue(view["hand_end_deadline"])
+        self.assertIsNotNone(view["last_hand"])
+        self.assertIn("award", view["last_hand"])
+
+
 if __name__ == "__main__":
     unittest.main()