feat: add hand detail API and enrich hand summary fields

- HandSummary: add hole_cards, starting_stacks, ending_stacks, pot_contributions
- Engine: capture all players' hole cards (not just showdown), pre/post hand stacks, per-level pot contributions
- Server: new GET /game/<game_id>/hands/<hand_number> route
- Service: add get_hand_state() method
- Tests: add ServerTests for new endpoint, update existing tests
- Existing GET /game/<game_id> auto-inherits new fields via shared to_dict()

tests/test_engine.py

@@ -100,10 +100,50 @@ class EngineTests(unittest.TestCase):
         awards = game._award_pots()
 
         self.assertEqual([award.amount for award in awards], [150, 100])
+        self.assertEqual(
+            [contribution["amount"] for contribution in game._last_pot_contributions],
+            [150, 100],
+        )
+        self.assertEqual(
+            game._last_pot_contributions[0]["contributors"],
+            {"p1": 50, "p2": 50, "p3": 50},
+        )
+        self.assertEqual(
+            game._last_pot_contributions[1]["contributors"],
+            {"p2": 50, "p3": 50},
+        )
         self.assertEqual(game.players[0].stack, 150)
         self.assertEqual(game.players[1].stack, 100)
         self.assertEqual(game.players[2].stack, 0)
 
+    def test_hand_summary_includes_full_hand_snapshots(self) -> None:
+        players = [
+            ("p1", "Player 1", CallingStationAgent()),
+            ("p2", "Player 2", CallingStationAgent()),
+            ("p3", "Player 3", CallingStationAgent()),
+        ]
+        game = TableGame("g5", players, starting_stack=100, small_blind=5, big_blind=10, rng=Random(23))
+
+        summary = game.run_hand()
+        payload = summary.to_dict()
+
+        self.assertEqual(set(summary.hole_cards), {"p1", "p2", "p3"})
+        self.assertTrue(all(len(cards) == 2 for cards in summary.hole_cards.values()))
+        self.assertEqual(summary.starting_stacks, {"p1": 100, "p2": 100, "p3": 100})
+        self.assertEqual(set(summary.ending_stacks), {"p1", "p2", "p3"})
+        self.assertEqual(sum(summary.starting_stacks.values()), sum(summary.ending_stacks.values()))
+        self.assertGreaterEqual(len(summary.pot_contributions), 1)
+        self.assertTrue(
+            all(
+                contribution["amount"] == sum(contribution["contributors"].values())
+                for contribution in summary.pot_contributions
+            )
+        )
+        self.assertEqual(set(payload["hole_cards"]), {"p1", "p2", "p3"})
+        self.assertEqual(payload["starting_stacks"], {"p1": 100, "p2": 100, "p3": 100})
+        self.assertIn("ending_stacks", payload)
+        self.assertIn("pot_contributions", payload)
+
     def test_short_all_in_does_not_reopen_raising_to_prior_actor(self) -> None:
         seen: list[tuple[str, str, list[str]]] = []
         players = [