refactor: extract signals filter builder, add ESLint 10 config, fix low-hanging issues

web/components/ChartCard/CardShell.tsx

@@ -12,12 +12,14 @@ export function Header({ title, onEdit, onDelete }: HeaderProps) {
       <span className="text-sm font-medium text-gray-200 truncate">{title}</span>
       <div className="flex gap-1 ml-2 shrink-0">
         <button
+          aria-label="Edit chart"
           onClick={onEdit}
           className="text-xs text-gray-400 hover:text-white px-1.5 py-0.5 rounded hover:bg-gray-700"
         >
           ✏️
         </button>
         <button
+          aria-label="Delete chart"
           onClick={onDelete}
           className="text-xs text-gray-400 hover:text-red-400 px-1.5 py-0.5 rounded hover:bg-gray-700"
         >
@@ -38,7 +40,7 @@ interface CardShellProps extends HeaderProps {
   empty: boolean;
   children: React.ReactNode;
   /** Ref to the div where the uPlot legend will be mounted */
-  legendContainerRef?: React.RefObject<HTMLDivElement>;
+  legendContainerRef?: React.RefObject<HTMLDivElement | null>;
 }
 
 export function CardShell({