Add E2E test for session.providerEndpoint.get

Validates the new shared API exposed by copilot-agent-runtime (see
github/copilot-sdk-internal#133) end-to-end from the Node SDK. Covers
both BYOK (returns provider config + headers) and CAPI (returns the
resolved CAPI base URL).

Regenerates rpc.ts and session-events.ts against the runtime schema that
adds the providerEndpoint RPC.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: SteveSandersonMS