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/register.py

@@ -1,14 +1,18 @@
 import asyncio
 from nonebot import on_command
 from nonebot.adapters.onebot.v11 import Bot, Event
-from . import (
+from .shared import (
     room_store, race_engine, config, logger,
     get_scope, check_access, get_event_id,
     _find_user_horse, _find_duplicate_horse, _get_horses_in_order,
     _format_horse_label, _send_to_scope, _build_race_image_message,
+    _get_user_name, _normalize_horse_name,
     run_race_with_settlement,
 )
-from ..models import HorseState, RoomState
+from ..models import HorseState, RoomState, Horse
+
+register_cmd = on_command("赛马报名", priority=5)
+
 
 @register_cmd.handle()
 async def handle_register(bot: Bot, event: Event):
@@ -25,7 +29,6 @@ async def handle_register(bot: Bot, event: Event):
     if not horse_name:
         scope = get_scope(event)
         horse_name = await _get_user_name(bot, scope, user_id)
-        # Ensure name is not too long when using nickname as default
         if len(horse_name) > 10:
             horse_name = horse_name[:10]
 
@@ -67,8 +70,3 @@ async def handle_register(bot: Bot, event: Event):
     count = len(room.horses)
     registered_horse = room.horses[horse_name]
     await register_cmd.finish(f"报名成功！{_format_horse_label(registered_horse)} 已加入比赛（{count}/8）")
-
-
-cancel_cmd = on_command("赛马取消报名", priority=5)
-
-