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/help.py

@@ -1,10 +1,16 @@
 from nonebot import on_command
 from nonebot.adapters.onebot.v11 import Bot, Event
-from . import config, logger, get_scope, check_access
+from .shared import config, get_scope, check_access
+
+help_cmd = on_command("赛马帮助", priority=5)
+
 
 @help_cmd.handle()
 async def handle_help(bot: Bot, event: Event):
     """Handle help command."""
+    if not await check_access(bot, event):
+        await help_cmd.finish("无权限访问此功能")
+        return
     help_text = f"""🏇 赛马游戏帮助
 
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