style(web): size + space the toolbar icon buttons to match the header

Make the server-list toolbar's expand/collapse toggle and open/close-monitoring
icons the same width and spacing as the header's theme / client-settings icons:

- ListToggle (default variant), PinColumnButton, and the MonitoringControls
  close button now render as `ActionIcon variant="subtle" size={36}` (glyph 20),
  matching the header's 36px ActionIcons, instead of wider `Button`s.
- ServerListControls uses `gap="sm"` so its buttons sit the same 12px apart as
  the header's RightSection controls.

Update a TaskListPanel test that found the toggle by a brittle
`mantine-Button-root` class to select it by its accessible name instead.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BrihGWcrM9JGRyu41nzZYw

clients/web/src/components/elements/ListToggle/ListToggle.tsx

@@ -1,4 +1,4 @@
-import { ActionIcon, Button } from "@mantine/core";
+import { ActionIcon } from "@mantine/core";
 import { RiExpandVerticalLine, RiCollapseVerticalLine } from "react-icons/ri";
 
 export interface ListToggleProps {
@@ -29,9 +29,16 @@ export function ListToggle({
     );
   }
 
+  // `size={36}` matches the header's theme / client-settings ActionIcons so the
+  // toolbar's toggle reads as the same size icon button.
   return (
-    <Button size="sm" variant="subtle" aria-label={label} onClick={onToggle}>
+    <ActionIcon
+      variant="subtle"
+      size={36}
+      aria-label={label}
+      onClick={onToggle}
+    >
       <Icon size={20} />
-    </Button>
+    </ActionIcon>
   );
 }