fix: add Discord OAuth token exchange logging for production diagnostics

- Log status code and response body when Discord /oauth2/token fails
- Helps identify why ExchangeCodeAsync returns null in production

Bump version → 2.8.1

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

.gitea/workflows/deploy.yml

@@ -6,7 +6,7 @@ on:
       - main 
 
 env:
-  VERSION: 2.8.0
+  VERSION: 2.8.1
 
 jobs:
   # ЧАСТЬ 1: Собираем образы и кладем в Gitea (чтобы делиться с ребятами)