fix(core): complete disclosure ARIA wiring in ChatToolCalls

[bhamodi]

Summary

ChatToolCalls had two incomplete disclosure relationships:

• Expandable call rows (CallRow, with resultDetail) render role="button" + tabIndex={0} and toggle an inline detail panel, but exposed no aria-expanded and no aria-controls, and the detail panel had no id. A screen-reader user heard a plain button with no indication it opens anything or what it controls.
• The tool-calls group header exposed aria-expanded but had no aria-controls, and its content region (the collapsible list of call rows) had no id -- so the toggle ↔ region relationship was implicit only.

This wires both up with useId()-generated ids:

• CallRow (ChatToolCalls.tsx:366): aria-expanded (only when the row is expandable) + aria-controls on the row, and id on the detail panel. The detail panel is conditionally mounted (rendered only while open), so aria-controls is set only while the panel is mounted -- it never points at a non-existent id. Matches the aria-controls={... ? ... : undefined} pattern used by the Date inputs (DateInput, etc.) for their conditionally-mounted popovers and the Banner fix (fix(core): link Banner expand toggle to its content via aria-controls #3719).
• Group header (ChatToolCalls.tsx:555): id on the always-mounted content region + aria-controls on the header. Because the region stays mounted (it collapses via CSS grid-template-rows, not unmount), aria-controls is unconditional -- matching SideNavItem.

Purely additive; no behavior/visual/role change.

Changes

• Chat/ChatToolCalls.tsx: useId() → aria-expanded/aria-controls on expandable call rows + id on the detail panel (set only while mounted); useId() → aria-controls on the group header + id on the content region.

Test plan

• node_modules/.bin/vitest run --root . packages/core/src/Chat -- 126 pass (10 files), including three new ChatToolCalls tests (the two disclosure tests confirmed failing before the fix):
  • exposes no aria-expanded on a call row without resultDetail -- a non-expandable row stays a plain row.
  • wires disclosure semantics on an expandable call row -- asserts aria-expanded="false" and no aria-controls while collapsed, then after click aria-expanded="true" and aria-controls resolving via document.getElementById to the panel containing the detail content.
  • points the group header aria-controls at the content region -- asserts the header's aria-controls resolves to the region containing the call rows.
• node_modules/.bin/tsc --project packages/core/tsconfig.json --noEmit -- clean.
• node_modules/.bin/eslint on changed files -- clean.

Notes

Found during a broader a11y audit of core components. Scoped to one fix per PR. Mirrors the sibling disclosure fixes on Banner (#3719) and Collapsible (#3707).

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[cixzhang]

Thanks @bhamodi — disclosure ARIA wiring matches DateInput + SideNavItem; conditional vs unconditional aria-controls both correct. 🙏