Adds the SDK-facing tools.invoke Gateway RPC for #74705.
Reuses the /tools/invoke policy path for tool policy, deny-list, owner filtering, before-tool-call hooks, session/agent scoping, and plugin approval handling. Returns typed SDK approval/refusal/success results while preserving HTTP compatibility and uses idempotencyKey as the stable tool-call id.
Includes protocol schema exports, method scope/list registration, SDK helper/types, docs, generated Swift models, tests, and changelog credit.