feat(api): improve Managed Agents APIs

- Filter sessions by attached memory store: GET /v1/sessions accepts a new
  optional `memory_store_id` query param
- BetaListUserProfilesResponse always returns `next_page` (now non-nullable
  in SDK types)
- Allow `max_tokens: 0` on message creation (previously rejected as below
  minimum)
- Rename "BYOC" to "self-hosted" in environment config docs
- Improve SDK reference docs: human-readable method summaries (e.g.
  "Delete a memory store"), richer parameter and field descriptions, and
  fuller enum docs across the managed-agents-memory beta
- CLI: accept `id` as an alias for memory-store, memory, agent, session,
  vault, environment, and credential identifiers on update commands for
  easier piping from stdin