dsh-attention-center: Move unprocessed events to the sidebar notification inbox

This DSH client plugin, maintained by kinfxhk, introduces a notification page in the left sidebar, centralizing four event types: task completion, pending approval, new inquiries, and pending proposal review. It supports filtering and clearing, utilizing icon blinking, number badges, and system notifications. The plugin requires DSH 0.2.1-rc.5 or later and is installed via `plugin_manager install_bundle` using a local directory; records are stored exclusively in localStorage.