dsh-model-account-login: DeepSeek Harness Model Account Persistent Authorization Plugin

`dsh-model-account-login` is a Cordis composition plugin designed to provide the UI for interactive login flows in DeepSeek Harness (DSH). It bridges the official authorization service over a host-side JSON-RPC channel, uses `AttemptRegistry` to manage login state, and persists sessions via `credentials` and `settings`. The web client provides a settings panel for managing login cards, device codes, external URLs, and hint messages. This plugin depends on DSH and related peer services and must be mounted via YAML patches.