docs: clarify recipient schemas and accept current region table headers

[JJasonSun]

Summary

Add the existing supported-feature list to recipient_result_schema, matching result_schema and the published Structured results guide. The region-table reader also accepts the two published fifth-column names, Default Line and Line Region, while retaining the source wording and all other validation.

Relates to CALLE-AI/awesome-phone-call-agents#477. This covers the missing schema-feature list only. Length/range/pattern keyword behavior and the scope of reserved-name/default-strictness rules still require backend-owner confirmation.

API contract

No new API behavior. The schema description repeats existing public guidance from content/guides/calls.mdx and the whole-task schema description. No executable call example, package release, or changeset.

Validation

Full local pnpm run validate passed against the current upstream region README using pnpm 8.10.2 and Python 3.12: typecheck, production build, static artifact checks, 11 deployment tests, and all 22 browser tests. Coverage includes parsing and rendering both supported table headers, exported snapshots, and malformed-source rejection. git diff --check passed.

These checks validate the documentation build and rendering, not untested server-side extraction semantics.

Checklist

• I kept the change focused and public-facing.
• I removed secrets, private URLs, phone numbers, and customer data.
• The OpenAPI description repeats existing published guidance.
• I updated tests for both supported region-table headers.
• No new layout; existing table rendering is preserved.
• I ran pnpm run validate.

[JJasonSun]

Publication is verified: the feature-list clarification is available in the public OpenAPI document. PR #61 repaired the deployment-list pagination check, and the production deployment passed.

The remaining schema semantics in CALLE-AI/awesome-phone-call-agents#477 still require backend-owner confirmation.