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()

texas_holdem/server.py

@@ -28,6 +28,14 @@ class PokerRequestHandler(BaseHTTPRequestHandler):
             if len(path) == 2 and path[0] in {"game", "games"}:
                 self._json(MANAGER.get_game_state(path[1]))
                 return
+            if len(path) == 4 and path[0] in {"game", "games"} and path[2] == "hands":
+                try:
+                    hand_number = int(path[3])
+                except ValueError:
+                    self._json({"error": "not found"}, HTTPStatus.NOT_FOUND)
+                    return
+                self._json(MANAGER.get_hand_state(path[1], hand_number))
+                return
             self._json({"error": "not found"}, HTTPStatus.NOT_FOUND)
         except KeyError as exc:
             self._json({"error": str(exc)}, HTTPStatus.NOT_FOUND)