feat: add disabled prop to FilterDropdown

[tmccoy14]

Summary

Adds an optional disabled prop to the FilterDropdown component. When true, the trigger button is unclickable and the dropdown cannot be opened. Defaults to false, so existing usage is unaffected.

Changes

• packages/ui — Added disabled?: boolean to FilterDropdownProps (defaults to false) and wired it to the trigger Button. A disabled button prevents the Radix DropdownMenuTrigger from opening the menu and picks up the Button's built-in disabled styling.
• packages/demo — Documented the new disabled prop in the Filter Dropdown props table.

Usage

<FilterDropdown
  label="Scope"
  options={options}
  selectedFilters={selectedFilters}
  onToggleFilter={onToggleFilter}
  onClearAll={onClearAll}
  disabled
/>