fix(discord): add missing Dapper.AOT reference to DiscordBot project

GmRelay.Shared references Dapper.AOT with PrivateAssets=all, which
prevents the runtime DLL from flowing to downstream projects. Telegram
bot works because it explicitly references Dapper.AOT directly, but
Discord bot did not — causing FileNotFoundException for Dapper.AOT
at runtime, breaking the scheduler and slash commands.

- Add Dapper.AOT 1.0.48 to GmRelay.DiscordBot.csproj
- Add regression test: DiscordWorkerProject_ShouldExist asserts
  Dapper.AOT is present in the DiscordBot csproj
- Bump version → 3.0.9

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

src/GmRelay.DiscordBot/GmRelay.DiscordBot.csproj

@@ -6,11 +6,14 @@
     <Nullable>enable</Nullable>
     <ImplicitUsings>enable</ImplicitUsings>
     <UserSecretsId>dotnet-GmRelay.DiscordBot-issue-26</UserSecretsId>
+    <!-- DiscordBot uses vanilla Dapper in its own handlers; DAP005 requires AOT-enabled Dapper -->
+    <NoWarn>$(NoWarn);DAP005</NoWarn>
   </PropertyGroup>
 
   <ItemGroup>
     <PackageReference Include="Aspire.Npgsql" Version="13.2.2" />
     <PackageReference Include="Dapper" Version="2.1.72" />
+    <PackageReference Include="Dapper.AOT" Version="1.0.48" />
     <PackageReference Include="Microsoft.Extensions.Hosting" Version="10.0.5" />
     <PackageReference Include="NetCord.Hosting" Version="1.0.0-alpha.489" />
     <PackageReference Include="NetCord.Hosting.Services" Version="1.0.0-alpha.489" />