refactor(mail): migrate to new pagination component
Replace johncms/johncms-pagination (LengthAwarePaginator) with Johncms\Http\Pagination across conversations, incoming/outgoing lists, attached files and contacts:
- MailMessageRepository: paginate*() -> count*()/get*(limit, offset); grouped conversations use distinct count + hydrateConversationUsers(); remove dead getIncomingGrouped/getOutgoingGrouped
- ContactRepository: paginateContacts() -> countContactList()/getContactList()
- 5 use cases split into count()/getPage()
- controllers: PaginationFactory + PaginationGuard + PageMeta
- drop total/pagination fields from Conversation/ConversationList/FileList/ContactList result DTOs
- MailMessageRepository: paginate*() -> count*()/get*(limit, offset); grouped conversations use distinct count + hydrateConversationUsers(); remove dead getIncomingGrouped/getOutgoingGrouped
- ContactRepository: paginateContacts() -> countContactList()/getContactList()
- 5 use cases split into count()/getPage()
- controllers: PaginationFactory + PaginationGuard + PageMeta
- drop total/pagination fields from Conversation/ConversationList/FileList/ContactList result DTOs