Add contacts, message status, and batch status methods

- get_message_status(id): query single message delivery status
- get_batch_status(batch_id): query all messages in a batch
- list_contacts(page, per_page, search, group_id): list contacts
- list_contact_groups(page, per_page): list contact groups
- New types: MessageStatus, BatchStatus, Contact, ContactGroup, PaginatedResponse

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

Bump version to 0.2.0

Initial release