fix: update theme config and remove env variable

backend/.env.production

@@ -13,7 +13,6 @@ FRONTEND_URL=https://goonblog.thevakhovske.eu.org
 # Database/Storage paths (relative to backend directory)
 POSTS_DIR=../public/posts
 THEMES_FILE=./themes.json
-SESSIONS_DIR=./sessions
 
 # Security Settings
 COOKIE_SECURE=true

backend/themes.json

@@ -1,5 +1,5 @@
 {
-  "activeTheme": "default",
+  "activeTheme": "minimal",
   "customThemes": [],
   "builtInThemes": [
     {