fix: use absolute paths for log files in all scripts

Fixed issue where log file redirections would fail when scripts change
directories. All scripts now use $PROJECT_ROOT/logs/... instead of
relative paths ./logs/...

This prevents errors like "Aucun fichier ou dossier de ce nom" when
scripts execute commands in different directories (e.g., checksum
verification in restore.sh).

Affected files:
- scripts/backup.sh
- scripts/restore.sh
- scripts/update.sh
- scripts/recover.sh

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

scripts/update.sh

@@ -10,7 +10,7 @@ cd "$PROJECT_ROOT"
 
 # Configuration des logs
 LOG_DIR="./logs"
-LOG_FILE="$LOG_DIR/update_$(date +%Y%m%d_%H%M%S).log"
+LOG_FILE="$PROJECT_ROOT/logs/update_$(date +%Y%m%d_%H%M%S).log"
 MAINTENANCE_ENABLED=false
 COMPOSE_BACKUP=""