refactor: remove slots and harden type boundaries

[K-Mistele]

Summary

• remove the deprecated Slot API in favor of Effect services through .task(), .spawn(), and .background()
• eliminate chained and unsafe source assertions by preserving generic relationships and parsing unknown persistence/RPC values
• make requirement-growing builders copy-on-write and expose a sound ActorHandle for heterogeneous registries
• tie cluster entities to their machine-owned RPC protocol and preserve typed client errors
• add transforming-codec, deferred-reply, persistence, and startup-failure regressions
• add a minor changeset for the intentional API changes

Intentional API changes

• remove Slot, slot schemas/types/errors, Machine.make({ slots }), ctx.slots, and slot provision options
• EntityMachine.layer accepts the MachineEntity returned by toEntity
• makeEntityActorRef(entity, client, entityId) receives the entity for reply decoding
• heterogeneous registry lookups expose ActorHandle
• transition and spawn-effect introspection expose guarded matches / run

Verification

• bun run lint
• bun run typecheck
• bun test --tsconfig-override=tsconfig.json — 299 passed
• bun run build
• git diff --check
• strict source audit for typescript/no-unsafe-type-assertion
• repeated independent defect-first reviews