dsh-safe-web-fetch: SSRF Protection WebFetch Plugin for DeepSeek Harness

`dsh-safe-web-fetch` is a DeepSeek Harness (DSH) plugin designed to mitigate SSRF security risks associated with `web_fetch`. It provides restricted network access without disrupting existing systems through strict DNS validation, connection isolation, redirect control, and content filtering. The plugin supports configuring request size limits, rate limits, and allowlists, making it suitable for developing intelligent agents in restricted environments. Developers can install and configure the plugin at the Profile layer to enable these security protections.