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>

compose.yaml

@@ -49,7 +49,7 @@ services:
         crond -f
 
   bot:
-    image: git.codeanddice.ru/toutsu/gmrelay-bot:3.0.7
+    image: git.codeanddice.ru/toutsu/gmrelay-bot:3.0.8
     restart: always
     depends_on:
       db:
@@ -67,7 +67,7 @@ services:
       retries: 3
 
   discord:
-    image: git.codeanddice.ru/toutsu/gmrelay-discord-bot:3.0.7
+    image: git.codeanddice.ru/toutsu/gmrelay-discord-bot:3.0.8
     restart: always
     depends_on:
       db:
@@ -84,7 +84,7 @@ services:
       retries: 3
 
   web:
-    image: git.codeanddice.ru/toutsu/gmrelay-web:3.0.7
+    image: git.codeanddice.ru/toutsu/gmrelay-web:3.0.8
     restart: always
     depends_on:
       db: