Add examples playground and explicit example typechecks

[SandroMaglione]

What changed

• add a standalone React and Vite examples playground
• add starter machines for turnstile, traffic-light, microwave, media-player, and worker/tab scenarios
• update the platformer example for the current schema collection API and full target construction
• give the platformer and Pokémon examples explicit typecheck scripts

Why

The repository benefits from small, focused examples that demonstrate the user-facing state-machine API and provide realistic places to exercise browser, React, worker, and statechart patterns.

Impact

The new playground is an independently installable example workspace. Existing library exports and runtime behavior are unchanged.

Validation

• pnpm format:check
• pnpm typecheck
• pnpm perf:types — all instantiation counts unchanged
• TypeScript typecheck and Vite production build for examples/platformer
• TypeScript typecheck and Vite production build for examples/pokemon
• TypeScript typecheck and Vite production build for examples/playground