Introducing the DeepSeek Harness IMAP Email Reading Plugin

`dsh-email-reader` is a DeepSeek Harness (DSH) plugin that provides email-reading capabilities to agents. It encapsulates the underlying IMAP protocol and supports listing, reading, and searching emails. Core features include automatic OAuth2 token refresh for Microsoft (the only supported method after September 2024), multi-account configuration, proxy support, and standardized error responses. The tools registered by this plugin are prefixed with `ol_email_` to avoid conflicts with marketplace plugins and to ensure that errors do not interrupt the host service.