docs: simplify call recipient examples

[Si40Code]

Summary

• sync the authoritative CALL-E Developer API OpenAPI snapshot from backend MR !113
• simplify the POST /v1/calls batch request example so recipients specify only required E.164 phone lists
• keep optional region and locale fields supported and documented by the schema

Backend MR: https://gitlab.airudder.com/s-eleven/s-eleven-mono/-/merge_requests/113

Public API impact

Backward-compatible documentation/example update only. No endpoint, request schema, SDK runtime behavior, or webhook behavior changes. The API reference example is the only public docs surface changed.

Validation

• pnpm run validate
• typecheck and production build passed
• deployment script tests: 11 passed
• Playwright docs tests: 16 passed
• no visual layout changes