feat(ncids): Implement Autocomplete combobox component

[Copilot]

Adds a fully accessible, generic Autocomplete combobox component per the WAI-ARIA APG combobox pattern, supporting both sync and async data sources.

Component API

// Sync options
<Autocomplete id="fruit" label="Fruit" options={fruits} onChange={setValue} />

// Async with debounce
<Autocomplete
  id="fruit"
  label="Fruit"
  loadOptions={(q) => fetchFruits(q)}
  debounceDelay={300}
  onChange={setValue}
/>

// Generic option shape
<Autocomplete<Country>
  id="country"
  label="Country"
  options={countries}
  getOptionLabel={(c) => c.name}
  getOptionValue={(c) => c.code}
  onChange={setValue}
/>

Key props (AutocompleteProps<T>)

Prop	Default	Description
options	—	Synchronous option list
loadOptions	—	Async loader; takes precedence over options
debounceDelay	300	ms before invoking loadOptions
renderOption	—	Custom option renderer (option, isHighlighted) => ReactNode
getOptionLabel / getOptionValue	option.label / option.value	Adapters for non-standard option shapes
noOptionsMessage	"No results found."	Empty-state text
loadingMessage	"Loading…"	Loading-state text
value	—	Controlled selected value

Accessibility

• Full ARIA combobox pattern: role="combobox", aria-expanded, aria-haspopup="listbox", aria-controls, aria-activedescendant, aria-labelledby
• Listbox always in DOM (toggled via hidden) so aria-controls always resolves
• Keyboard: ↑/↓ highlight, ArrowUp from first item clears highlight, Enter selects, Escape closes, Tab closes

Files

• Autocomplete.tsx — component + exported AutocompleteProps<T> / AutocompleteOption
• Autocomplete.module.scss — USWDS-aligned CSS module
• Autocomplete.test.tsx — 25+ unit tests + vitest-axe a11y tests (open and closed states)
• Autocomplete.stories.tsx — 6 Storybook stories (sync, async, custom renderer, custom shape, disabled, controlled)
• Autocomplete/index.ts + ncids/index.ts updated barrel exports

[github-actions]

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