ytaudio: rename join/leave -> ytjoin/ytleave to avoid command collisions

The Minecraft cog already registers top-level 'join' and 'leave', which
caused a CommandRegistrationError. Namespace these two commands under a
yt-prefix (ytjoin, ytleave, alias ytdc).

ytaudio/ytaudio.py

@@ -371,14 +371,14 @@ class YTAudio(commands.Cog):
             pass
         await ctx.send(f"🔊 Volume set to {level}.")
 
-    @commands.command()
+    @commands.command(name="ytjoin")
     @commands.guild_only()
     async def join(self, ctx: commands.Context):
         """Join your voice channel."""
         if await self._ensure_connected(ctx):
             await ctx.send("✅ Joined.")
 
-    @commands.command(aliases=["disconnect", "dc"])
+    @commands.command(name="ytleave", aliases=["ytdc"])
     @commands.guild_only()
     async def leave(self, ctx: commands.Context):
         """Leave the voice channel and clear state."""