dsh-rule-manager: DeepSeek Harness Unified Rule Management Plugin

The DSH plugin dsh-rule-manager integrates global and project rule editing along with LLM-based automatic rule splitting into a unified web interface, replacing the fragmented legacy plugins. Users can intuitively edit global rules, manage project-specific rules, or use an LLM to split lengthy rules into a concise summary and skill files, with support for overwrite or merge modes. This plugin consolidates the legacy functionality; the older plugin must be uninstalled before installation, and each operation is limited to 256 KiB.