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>

AGENTS.md

@@ -167,6 +167,13 @@ Keyboard behavior:
 
 Support Ctrl+Plus and Ctrl+Shift+Plus for insertion.
 
+Editor actions use `IconButton` (`src/frontend/components/icon-button.tsx`,
+`lucide-react` icons). The German action text is always the accessible name and
+tooltip; the toolbar shows icon plus text, group headers and rows show icons
+only, separated into logical blocks with `IconButtonSeparator`. Destructive
+actions use `variant="danger"` (trash icon for circuits and groups, `ListX` for
+removing a device row).
+
 ## Bootstrap / Styling Rule
 
 Bootstrap may be used for the general application UI, such as navigation, page layout, buttons, forms, cards, alerts and modals.