fix(discord): add console logging and deferred responses

- Add builder.Logging.AddConsole() to DiscordBot Program.cs so logs
  are visible in docker logs.
- Add granular LogInformation/LogError calls to DiscordNewSessionCommand
  and DiscordRescheduleCommand to diagnose failures.
- Use InteractionCallback.DeferredMessage() + ModifyResponseAsync pattern
  for /newsession and /reschedule to avoid Discord 3-second interaction
  timeout.
- Bump version → 3.0.8

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

Directory.Build.props

@@ -1,6 +1,6 @@
 <Project>
   <PropertyGroup>
-    <Version>3.0.7</Version>
+    <Version>3.0.8</Version>
     <TargetFramework>net10.0</TargetFramework>
     <LangVersion>preview</LangVersion>
     <Nullable>enable</Nullable>