Add transition snapshots and structural metadata

[SandroMaglione]

Summary

• expose one fully typed, read-only full logical snapshot to event, eventless, and completion transition contexts, captured at the beginning of each microstep and shared across simultaneous parallel transitions
• add serializable Machine.activityDefinitions metadata for process invokes, Effects, timers, child machines, and unevaluated dynamic factories, and render owned activities in the structural text visualization
• resolve Effect Schema annotations into Machine.stateNodes, support descriptive annotations on choice/history pseudo-states, and use titles as display labels without changing structural identity
• document the context, lifecycle, inspection, and annotation contracts and add focused runtime, property, compiler, and visualization coverage

Changeset

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

Added .changeset/rich-machines-inspect.md as a minor change.

Validation

• pnpm check
• Relevant example checks, when examples changed
• Reviewed the automated type-performance report, when the public TypeScript API or inference changed

No example package changed, so no example-local check was required.

Additional validation:

• pnpm perf:types
• 335 runtime tests passed
• 574 type assertions passed
• strict consumer and package verification passed
• generated activity invariants cover timer metadata agreement and real state-node ownership