fix: break circular import in horse racing commands

Extract shared.py from commands/__init__.py to break circular dependency:
- shared.py: shared variables/services/helper functions
- access.py: get_scope/check_access/get_event_id (canonical source)
- __init__.py: re-exports from shared.py for backward compat
- register/bet/race/help: import from .shared instead of package

danding_bot/plugins/group_horse_racing/commands/bet.py

@@ -1,11 +1,16 @@
 from nonebot import on_command
 from nonebot.adapters.onebot.v11 import Bot, Event
-from . import (
+from .shared import (
     room_store, points_service, config, logger,
     get_scope, check_access, get_event_id,
     _resolve_horse_selector, _format_horse_label,
+    _get_horses_in_order, _find_user_horse,
     calculate_odds,
 )
+from ..models import RoomState, Bet
+
+cancel_cmd = on_command("赛马取消报名", priority=5)
+
 
 @cancel_cmd.handle()
 async def handle_cancel(bot: Bot, event: Event):
@@ -85,7 +90,6 @@ async def handle_cancel_bet(bot: Bot, event: Event):
                 logger.error(f"退还下注失败 user={bet.user_id} amount={bet.amount}: {e}")
                 refund_errors.append(bet)
 
-        # 只移除已成功退还的下注
         if refund_errors:
             failed_amount = sum(b.amount for b in refund_errors)
             room.bets = [b for b in room.bets if b.user_id != user_id or b in refund_errors]
@@ -180,8 +184,3 @@ async def handle_odds(bot: Bot, event: Event):
     lines.append(f"总下注池: {total_bet}")
 
     await odds_cmd.finish("\n".join(lines))
-
-
-race_list_cmd = on_command("赛马列表", priority=5)
-
-