Render Resource Links visually like V1 (expandable, click-to-read)

[cliffhall]

Background

V2's resource_link content rendering is currently a placeholder. In clients/web/src/components/elements/ContentViewer/ContentViewer.tsx the resource_link case just renders the name/uri as plain blue text:

case "resource_link":
  return (
    <Stack gap="xs">
      <Text size="sm" c="blue">
        {block.name ?? block.uri}
      </Text>
    </Stack>
  );

V1 has a much richer treatment in client/src/components/ResourceLinkView.tsx (rendered from ToolResults.tsx). We should bring that experience to V2 (Mantine-native, following V2 conventions).

What V1 does (the target behavior)

ResourceLinkView renders each resource_link as an interactive, expandable card showing:

• The URI (monospace, link-styled).
• Optional name (emphasized).
• Optional description.
• A mimeType badge when present.
• An expand/collapse affordance (▶ / ▼, with a loading spinner) that, on click/Enter/Space, calls onReadResource(uri) to fetch the linked resource and inline its content below the card.
• Accessible: role="button", aria-expanded, aria-label, keyboard handlers, focus ring.

Scope (V2)

• Replace the placeholder resource_link branch in ContentViewer with a proper presentation showing uri / name / description / mimeType.
• Make it expandable with a read-on-demand action that fetches the resource and renders its content inline (reuse the existing V2 resource content rendering, e.g. ContentViewer/resource content components, rather than V1's JsonView).
• Wire the read-resource callback through the relevant props so the host (tool result panel, etc.) can supply the read handler — follow the V2 "dumb component + callbacks as props" pattern.
• Use Mantine components, theme variants, and --inspector-* tokens per the project conventions (no raw hex, no inline styles, no Tailwind classes carried over from V1).
• Add an element/story under src/components/elements/ if it warrants its own documented component (e.g. ResourceLink), with Storybook coverage.

Acceptance criteria

• A resource_link in tool results (and anywhere ContentViewer renders) shows uri, name, description, and mimeType (when present).
• The link is expandable and reads the resource on demand, rendering its content inline; collapse hides it again.
• Keyboard accessible and consistent with V2 styling conventions.
• Unit tests cover the collapsed/expanded states and the read-on-demand callback; npm run validate, test:integration, and test:storybook pass.

References

• V1: client/src/components/ResourceLinkView.tsx, client/src/components/ToolResults.tsx
• V2: clients/web/src/components/elements/ContentViewer/ContentViewer.tsx