Beta: memory/environment APIs removed, RefusalCategory enum narrowed

BreakingBreaking change

This is a breaking change — integrations that rely on the affected behaviour will need updates before the change rolls out.

What changed

This diff makes several breaking changes to the Beta API surface:

The /v1/memory_stores/{memory_store_id}/memories?beta=true endpoint (POST BetaCreateMemory) is removed and replaced by a new /v1/sessions?beta=true endpoint (BetaCreateSession).
Environment webhook paths (environment.created, environment.updated, environment.archived, environment.deleted) and memory store webhook paths (memory_store.created, memory_store.archived, memory_store.deleted) are removed from the spec entirely, along with their corresponding schemas and discriminator mappings.
The RefusalCategory enum loses the "military_weapons" value, which is a breaking change for any code that handles that enum value.
requestBody is now marked required: true on the skill-creation endpoints (clarification, not a behaviour change in practice).