Collapse ServerSettingsForm into accordion and add subtle ListToggle variant

Wraps every section of ServerSettingsForm (Connection Mode, Custom
Headers, Request Metadata, Timeouts, OAuth Settings) in a controlled
Mantine Accordion. The accordion is driven by new required
`expandedSections` / `onExpandedSectionsChange` props so the parent
owns expand/collapse state — consistent with the dumb-component
principle.

Adds a `variant?: "default" | "subtle"` prop to ListToggle. In subtle
mode it renders as an ActionIcon with `variant="subtle"`, `color="gray"`,
and a 16px icon so it visually matches Mantine's CloseButton in modal
headers (transparent until hover).

Adds a WithSettingsModal story on UnconnectedView that presents the
form inside a Mantine Modal with a custom three-column header: subtle
ListToggle on the left (expands/collapses all sections at once),
"Server Settings" Title centered, CloseButton on the right.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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

@@ -23,3 +23,19 @@ export const Collapsed: Story = {
     onToggle: fn(),
   },
 };
+
+export const SubtleExpanded: Story = {
+  args: {
+    compact: false,
+    variant: "subtle",
+    onToggle: fn(),
+  },
+};
+
+export const SubtleCollapsed: Story = {
+  args: {
+    compact: true,
+    variant: "subtle",
+    onToggle: fn(),
+  },
+};

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

@@ -1,14 +1,27 @@
-import { Button } from "@mantine/core";
+import { ActionIcon, Button } from "@mantine/core";
 import { RiExpandVerticalLine, RiCollapseVerticalLine } from "react-icons/ri";
 
 export interface ListToggleProps {
   compact: boolean;
   onToggle: () => void;
+  variant?: "default" | "subtle";
 }
 
-export function ListToggle({ compact, onToggle }: ListToggleProps) {
+export function ListToggle({
+  compact,
+  onToggle,
+  variant = "default",
+}: ListToggleProps) {
   const Icon = compact ? RiExpandVerticalLine : RiCollapseVerticalLine;
 
+  if (variant === "subtle") {
+    return (
+      <ActionIcon variant="subtle" color="gray" size="md" onClick={onToggle}>
+        <Icon size={16} />
+      </ActionIcon>
+    );
+  }
+
   return (
     <Button size="sm" onClick={onToggle}>
       <Icon size={20} />