feat(react): add the Switch primitive

[ivanbanov]

Summary

Adds the Switch primitive as two packages:

• @dunky.dev/switch — the framework-free core: a state machine (built on @dunky.dev/state-machine) owning the checked/unchecked graph, the disabled guard, and the connect that exposes parts and reactions.
• @dunky.dev/react-switch — the thin React binding rendering the compound component on top of the core connect.

A switch is a binary on/off control that takes effect immediately (airplane mode, dark theme), following the WAI-ARIA APG switch pattern. Checked state is exposed both controlled and uncontrolled, and every toggle is reported back through onCheckedChange.

Anatomy

<Switch>          - root; owns checked state, renders nothing of its own
  |_ <Control>    - the interactive element: switch role + checked state
  |  |_ <Thumb>   - the knob; purely visual, styled off data-state
  |_ <Label>      - names the control; pressing it toggles

Behavior

• The Control carries role="switch" with aria-checked always true or false — never mixed.
• Space toggles (and Enter, via the natively activatable element); control press, label press, and keyboard activation all send the same toggle intent.
• The Label is not a native <label>: it carries its own press binding and names the control through aria-labelledby, which only ever references a rendered Label.
• Disabled gates user intent in the machine — control and label alike — and is exposed as aria-disabled; controlled/programmatic changes still apply so consumer state never desyncs.
• Every part carries data-state="checked" | "unchecked" and data-disabled as styling/animation hooks.

Test plan

• pnpm test:ci
• pnpm typecheck
• pnpm lint
• pnpm format:check
• pnpm build

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