dsh-prompt-switcher: Local Prompt Template Sync via WebDAV

`dsh-prompt-switcher` is a web plugin designed specifically for DeepSeek Harness (DSH) to address gaps in local Markdown prompt template management and cross-device synchronization. It supports quick selection of local `.md` templates using the `/` command, with templates either applied globally or appended after the global prompt. It also provides environment variable substitution, WebDAV cloud synchronization, and session deletion. Installation requires DSH >= 0.1.7-alpha.1, and the service must be restarted after installation. The plugin runs in ESM mode and is suitable for users who need to manage Prompts centrally and achieve cloud synchronization.