feat(react): add the Select primitive

[ivanbanov]

Summary

Adds the Select primitive as two packages:

• @dunky.dev/select — the framework-free core: a state machine (built on
  @dunky.dev/state-machine) that owns value + open state, option
  registration, highlight navigation, typeahead, and selection.
• @dunky.dev/react-select — the thin React binding that renders the
  compound parts and wires DOM events into the machine.

A single-choice dropdown listbox following the WAI-ARIA select-only combobox
pattern. Value and open state are each controlled or uncontrolled; every
value, open, and highlight change is reported through onValueChange /
onOpenChange / onHighlightChange.

Anatomy

<Select>                   - root; owns value + open state, renders nothing of its own
  |_ <Trigger>             - the button that shows the choice and opens the list;
  |  |                       keyboard focus lives here the whole time
  |  |_ <Value>            - the selected option's label, or a placeholder
  |_ <Listbox>             - the popup list of options
     |_ <Item>             - one option; registers itself with the machine
        |_ <ItemIndicator> - the "this one is chosen" mark, rendered only
                             inside the selected item

Behavior

• Focus model: DOM focus stays on the trigger the whole time; while open,
  aria-activedescendant names the highlighted option — the APG select-only
  combobox model (one tab stop, no focus jumps on open/close).
• Roles: trigger is a combobox with aria-haspopup="listbox",
  aria-expanded, and aria-controls; the popup is a listbox of options
  carrying aria-selected / aria-disabled.
• Keyboard: Enter/Space/ArrowUp/ArrowDown open (highlighting the selected
  option, else the first enabled); Home/End open pinned to the first/last.
  While open, arrows move the highlight across enabled options (wrapping when
  loop), Enter/Space select and close, Escape/Tab/outside interaction close
  without selecting.
• Typeahead: printable characters accumulate into a machine-owned buffer
  (1s reset) with case-insensitive prefix matching; a repeated character
  cycles through options starting with it.
• Items register themselves from the render tree (value, label, disabled),
  so the option list always mirrors what is rendered; disabled items are
  skipped by navigation and typeahead.

Test plan

• pnpm test:ci — 162 tests passing
• pnpm typecheck
• pnpm lint
• pnpm format:check
• pnpm build

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