fix(bus): tighten GlobalBus payload and BusEvent.define types

Constrain BusEvent.define to ZodObject instead of ZodType so TS knows
event properties are always a record. Type GlobalBus payload as
{ type: string; properties: Record<string, unknown> } instead of any.

Refactor watcher test to use Bus.subscribe instead of raw GlobalBus
listener, removing hand-rolled event types and unnecessary casts.