Migrate examples to machine event constructors

[SandroMaglione]

Summary

• Replace every remaining Event.cases.<Tag>.make(...) call under examples/ with the protocol-bound event construction APIs.
• Use Machine.events for public UI and planner delivery and Machine.internalEvents for timers, raised events, invoke results, and snapshot mappings.
• Keep decoded Machine.event construction at model-trace and Worker/BroadcastChannel boundaries, where events must remain inspectable or structured-cloneable.
• Split the media-player definition from its handlers so invocation helpers can share machine-owned internal constructors without a module cycle.

Changeset

• Added or updated for a library or package-metadata change
• Not required because this PR does not change src/ or package.json

Validation

• pnpm check
• examples/platformer: pnpm check
• examples/playground: pnpm check
• Automated type-performance measurement passed or was not required (pnpm perf:types passed locally)
• Automated runtime- and memory-performance measurement passed or was not required (pnpm perf:runtime completed locally)