Add password validation with i18n support and GitHub button improvements

- Add password field to UserUpdate schema for password change on edit
- Implement password validation in update_user endpoint
- Add i18n translations for password validation errors (ru/en)
- Update SecurityService.validate_password to support language parameter
- Add GitHub icon and repository name 'pvemanager' to header button
- Fix internal server error when updating user password
- Clean up hardcoded translations in frontend

backend/.env.example

@@ -28,3 +28,10 @@ DEFAULT_SSH_PORT=22
 # Security
 CORS_ORIGINS=*
 ALLOWED_HOSTS=localhost,127.0.0.1
+
+# Update Check Configuration
+# Set to true to disable update checks for private repositories
+DISABLE_UPDATE_CHECK=false
+# GitHub token for private repositories (optional)
+# Get token at: https://github.com/settings/tokens (needs 'repo' scope)
+GITHUB_TOKEN=