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/groups/TaskListPanel/TaskListPanel.test.tsx

@@ -169,13 +169,12 @@ describe("TaskListPanel", () => {
       screen.getAllByRole("button", { name: "Collapse" }).length,
     ).toBeGreaterThan(0);
 
-    const buttons = screen.getAllByRole("button");
-    const toggle = buttons.find(
-      (b) =>
-        b.textContent === "" && b.classList.contains("mantine-Button-root"),
-    );
-    expect(toggle).toBeDefined();
-    await user.click(toggle!);
+    // The ListToggle is labelled "Collapse all" / "Expand all" — distinct from
+    // the per-entry "Collapse" / "Expand" buttons.
+    const toggle = screen.getByRole("button", {
+      name: /Collapse all|Expand all/,
+    });
+    await user.click(toggle);
 
     // After toggle, entries collapsed — they show Expand
     expect(