Connect an inbox by forwarding

Creates a connected mailbox at the inbox's own address and answers with a forwarding address on the platform's forwarding domain, with the steps for Gmail, Outlook and other providers. Add a forwarding rule at the provider; what arrives at that address is unwrapped (original sender, date, subject) and stored under the connected mailbox. Gmail asks the forwarding address to confirm: the code and the link appear on the connection. The first mail that comes back, or a probe (POST /api/emails/{address}/connector/verify), makes the connection active. Only new mail arrives this way; older mail cannot be imported. Requires email:write. The forwarding domain must be configured on the server.