fix: replace decorator misuse with MaintenanceAwareTree subclass (#82)

Closes #82

`@self.tree.interaction_check` in `setup_hook` called the coroutine as
a decorator factory instead of overriding it — producing an unawaited
coroutine warning and leaving maintenance mode as a no-op.

Replace with `MaintenanceAwareTree(discord.app_commands.CommandTree)` that
overrides `interaction_check`, and pass `tree_cls=MaintenanceAwareTree`
to `super().__init__`. Remove the now-obsolete decorator block from
`setup_hook`.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

bot.py

@@ -64,6 +64,25 @@ def setup_logging():
     return logger
 
 
+class MaintenanceAwareTree(discord.app_commands.CommandTree):
+    """CommandTree subclass that blocks non-admin users when maintenance mode is active."""
+
+    async def interaction_check(self, interaction: discord.Interaction) -> bool:
+        bot = interaction.client
+        if not getattr(bot, "maintenance_mode", False):
+            return True
+        if (
+            isinstance(interaction.user, discord.Member)
+            and interaction.user.guild_permissions.administrator
+        ):
+            return True
+        await interaction.response.send_message(
+            "🔧 The bot is currently in maintenance mode. Please try again later.",
+            ephemeral=True,
+        )
+        return False
+
+
 class SBABot(commands.Bot):
     """Custom bot class for SBA league management."""
 
@@ -77,6 +96,7 @@ class SBABot(commands.Bot):
             command_prefix="!",  # Legacy prefix, primarily using slash commands
             intents=intents,
             description="Major Domo v2.0",
+            tree_cls=MaintenanceAwareTree,
         )
 
         self.logger = logging.getLogger("discord_bot_v2")
@@ -86,22 +106,6 @@ class SBABot(commands.Bot):
         """Called when the bot is starting up."""
         self.logger.info("Setting up bot...")
 
-        @self.tree.interaction_check
-        async def maintenance_check(interaction: discord.Interaction) -> bool:
-            """Block non-admin users when maintenance mode is enabled."""
-            if not self.maintenance_mode:
-                return True
-            if (
-                isinstance(interaction.user, discord.Member)
-                and interaction.user.guild_permissions.administrator
-            ):
-                return True
-            await interaction.response.send_message(
-                "🔧 The bot is currently in maintenance mode. Please try again later.",
-                ephemeral=True,
-            )
-            return False
-
         # Load command packages
         await self._load_command_packages()