Document the granted companies endpoints in the Preview API (#659)

* Document the granted-companies endpoints in the Preview API

Adds GET/PUT/DELETE /contacts/{contact_id}/granted_companies to
descriptions/0/api.intercom.io.yaml, matching the Preview spec in
developer-docs.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

* Fix granted companies spec inconsistencies

Drops the per_page maximum, since values above it are reduced rather than
rejected; makes pages nullable so the replace response validates; and
removes the omitted-field request example, which could not validate against
a schema that requires company_ids.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

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Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: laszlobogacsi-intercom