Use icon buttons in the circuit list editor

- New IconButton/IconButtonSeparator component based on lucide-react.
- Toolbar: icon plus text, grouped into history, view and insert blocks.
- Group headers: compact icons for add circuit, upstream fuse (VS), group
  RCD (FI), edit, move up/down, renumber and delete; the header no longer
  overflows the grid.
- Rows: add device, delete circuit (trash) and delete device (ListX).
- The previous German labels remain accessible names and tooltips;
  destructive actions highlight in the danger color.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/frontend/components/icon-button.tsx

@@ -0,0 +1,59 @@
+"use client";
+
+import type { LucideIcon } from "lucide-react";
+import type { ReactNode } from "react";
+
+/**
+ * Compact editor button with a lucide icon. `label` is always the accessible
+ * name; it is also the tooltip unless a more specific `title` is given.
+ * With `showLabel` the label (or `children`) is rendered next to the icon.
+ */
+export function IconButton({
+  icon: Icon,
+  label,
+  title,
+  onClick,
+  disabled,
+  variant = "default",
+  showLabel = false,
+  children,
+  className,
+  tabIndex,
+  ariaExpanded,
+  ariaControls,
+}: {
+  icon: LucideIcon;
+  label: string;
+  title?: string;
+  onClick: () => void;
+  disabled?: boolean;
+  variant?: "default" | "danger" | "primary";
+  showLabel?: boolean;
+  children?: ReactNode;
+  className?: string;
+  tabIndex?: number;
+  ariaExpanded?: boolean;
+  ariaControls?: string;
+}) {
+  return (
+    <button
+      aria-controls={ariaControls}
+      aria-expanded={ariaExpanded}
+      aria-label={showLabel ? undefined : label}
+      className={`icon-button icon-button-${variant}${className ? ` ${className}` : ""}`}
+      disabled={disabled}
+      onClick={onClick}
+      tabIndex={tabIndex}
+      title={title ?? label}
+      type="button"
+    >
+      <Icon aria-hidden="true" size={15} strokeWidth={2} />
+      {showLabel ? <span>{children ?? label}</span> : children}
+    </button>
+  );
+}
+
+/** Thin vertical divider between groups of icon buttons. */
+export function IconButtonSeparator() {
+  return <span aria-hidden="true" className="icon-button-separator" />;
+}