dsh-imessage: Adding a Photon-Hosted iMessage Channel to DeepSeek Harness

`dsh-imessage` is a plugin for DeepSeek Harness (DSH) designed to enable bidirectional interaction between iMessage text and DSH sessions via the Photon-hosted iMessage transport layer. This plugin allows users to automatically convert received iMessage text into DSH Prompts and send the final assistant responses generated by DSH back through iMessage. Core functionalities include completing device code authorization on the `Settings → iMessage` page, configuring the sender's E.164 number, and obtaining the hosted number; supporting commands such as `/new`, `/switch`, and `/approve` to control session states and manual approval; automatically filtering unauthorized messages; and converting M...