fix(discord): cast COUNT to int for slash command list query

PostgreSQL COUNT() returns bigint, but DiscordSessionListItemDto expects
int for PlayerCount and WaitlistCount. Dapper 2.1.72 in GmRelay.DiscordBot
(without Dapper.AOT) fails to materialize the record with bigint→int mismatch.
Added ::int casts to both COUNT expressions.

Bump version to 3.0.6.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Directory.Build.props

@@ -1,6 +1,6 @@
 <Project>
   <PropertyGroup>
-    <Version>3.0.5</Version>
+    <Version>3.0.6</Version>
     <TargetFramework>net10.0</TargetFramework>
     <LangVersion>preview</LangVersion>
     <Nullable>enable</Nullable>