fix(server): race WebSocket, SVG refusé, rows.Err, time.NewTicker

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/db/db.go

@@ -117,6 +117,9 @@ func (d *DB) GetAgents() ([]models.Agent, error) {
 		}
 		agents = append(agents, a)
 	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
 	return agents, nil
 }
 
@@ -143,6 +146,9 @@ func (d *DB) GetMetricsHistory(agentID string, from, to int64) ([]map[string]int
 			"hdd_used": hddUsed, "hdd_total": hddTotal,
 		})
 	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
 	return result, nil
 }