refactor: replace PostgreSQL placeholders with generic SQL syntax and add audit logging for duplicate entries

- Replace $%d placeholders with ? in logsHandler for database abstraction
- Remove unused argIndex variable in auth.go
- Log duplicate permanent whitelist insertions to audit_log in db.go

auth.go

@@ -136,7 +136,6 @@ func logsHandler(cfg Config, db *sql.DB) http.HandlerFunc {
 
 		query := `SELECT timestamp, action, ip, cidr, ttl_seconds, reason, api_client_ip FROM audit_log`
 		var args []any
-		argIndex := 1
 
 		filterAction := r.URL.Query().Get("action")
 		filterIP := r.URL.Query().Get("ip")
@@ -145,14 +144,12 @@ func logsHandler(cfg Config, db *sql.DB) http.HandlerFunc {
 
 		var conditions []string
 		if filterAction != "" {
-			conditions = append(conditions, fmt.Sprintf(`action = $%d`, argIndex))
+			conditions = append(conditions, `action = ?`)
 			args = append(args, filterAction)
-			argIndex++
 		}
 		if filterIP != "" {
-			conditions = append(conditions, fmt.Sprintf(`ip = $%d`, argIndex))
+			conditions = append(conditions, `ip = ?`)
 			args = append(args, filterIP)
-			argIndex++
 		}
 
 		if len(conditions) > 0 {