ToolDetailPanel: collapse long descriptions + scroll the SchemaForm inside its own container

[cliffhall]

Problem

When a tool ships with a very long description (e.g. sequential-thinking-server's "Sequential Thinking" tool — see the screenshot below), the ToolDetailPanel body grows past its container's height and pushes the form + Execute Tool button off the bottom of the screen. The ToolsScreen is correctly viewport-bounded (ScreenLayout uses h: "calc(100vh - var(--app-shell-header-height, 0px))" at clients/web/src/components/screens/ToolsScreen/ToolsScreen.tsx:28-34), so we want to keep that constraint and instead make the panel respect it.

Repro: open sequential-thinking-server in v2/main, select the "Sequential Thinking" tool. Description fills most of the viewport; the form fields below it are clipped at the bottom of the panel and the Execute Tool button is off-screen.

Screenshot

Proposed change

Two coordinated edits to clients/web/src/components/groups/ToolDetailPanel/ToolDetailPanel.tsx:

1. Collapsible description

Wrap the existing <DescriptionText>{description}</DescriptionText> (line 101) in a Mantine <Collapse in={descriptionOpen}>. Expose the trigger as a chevron icon on the right side of the tool name row, not as a separate button:

• Anchor inside <TitleRow> (lines 80-83). Add a third child after <ToolTitle> that is the chevron toggle. The row is already wrap: "nowrap" with miw: 0, so the chevron will pin to the right edge naturally — give the title flex: 1 to absorb the slack, or wrap the title + chevron in a Group justify="space-between".
• Icon set: react-icons/fa (already a project dependency — see e.g. react-icons/md and react-icons/ri already in use in AppListItem.tsx:2, ServerAddMenu.tsx:2, etc.):
  • FaChevronRight when description is collapsed (default state — long descriptions are the common case for the gnarly tools).
  • FaChevronDown when expanded.
• Use an UnstyledButton or ActionIcon with aria-label="Show description" / "Hide description" so screen readers can announce the state change.
• Only render the chevron when a description actually exists (description truthy). If there's no description, no chevron, no Collapse.
• Default state: collapsed. Reset to collapsed on tool change so switching tools doesn't carry over the expanded state — the selectedToolName change in ToolsScreen.tsx:84-87 already clears formValues; mirror that for the panel's local "expanded" state.

2. Internal scroll for the SchemaForm region

The Execute Tool button (lines 114-124) must stay visible at the bottom of the panel regardless of how long the schema is. Wrap the <SchemaForm> (lines 105-110) + <ProgressDisplay> (line 112) in a ScrollArea.Autosize (or equivalent) so they scroll inside a bounded region while the panel's chrome (title row, annotations, description-when-expanded, divider, button row) stays pinned.

• Use the same idiom we landed in the Connection Info modal's instructions block (clients/web/src/components/groups/ConnectionInfoContent/ConnectionInfoContent.tsx:138): <ScrollArea.Autosize mah={…}>. Pick mah so the panel always lands flush with the same bottom margin as ResourcesScreen / PromptsScreen / ServerListScreen — i.e. it should match the ScreenLayout's p: "xl" padding at the bottom rather than spilling under it.
• The outer <Stack> (line 79) probably needs h: "100%" so it fills the ContentCard and lets the ScrollArea claim the remaining vertical space. The ContentCard itself is flex={1} in ToolsScreen.tsx:92, which already gives it the viewport-bounded height the ScrollArea needs.

Acceptance criteria

• Loading a tool with a long description renders the description collapsed by default with FaChevronRight to the right of the tool name.
• Clicking the chevron expands the description (with the Mantine Collapse animation) and the icon flips to FaChevronDown.
• Switching to a different tool resets the description to collapsed.
• When the SchemaForm has many fields (or progress output), it scrolls inside its own container — the title row, annotations, description, divider, and Execute Tool button row remain pinned and never leave the viewport.
• The bottom of the ToolDetailPanel lands at the same baseline as other screens (matching ScreenLayout's p: "xl" bottom padding).
• Tools with no description still render the title row cleanly — no orphaned chevron.
• Existing ToolDetailPanel.test.tsx and .stories.tsx updated to cover both states (collapsed default + expanded toggle) and the internal-scroll wiring.
• npm run validate + npm run test:storybook pass.

Notes

• Collapse and ScrollArea both come from @mantine/core — no new dependency surface.
• Per project conventions: define the chevron button as a withProps subcomponent constant (e.g. const DescriptionToggle = ActionIcon.withProps({ variant: "subtle", "aria-label": …, size: "sm" })) rather than inline props.
• This is a polish item, not a blocker for new tool development — Backlog or Fit and Finish column on the V2 board, whichever you prefer.

Screenshot

(Attached by the requester — Sequential Thinking tool's description filling the middle column with the form clipped at the bottom.)