dsh-plugin-uisfx: Add semantic UI sound effects for DeepSeek Harness

dsh-plugin-uisfx is a plugin designed for the DeepSeek Harness (DSH) Web environment, maintained by XanthanL and released under the MIT License. By embedding the uisfx 0.4.0 Web Audio synthesis runtime, the plugin provides semantic sound feedback for task statuses and button actions without requiring built-in audio files. Its core features include 12 global sound effect packages, 11 scene mappings, real-time preview, automatic sound feedback for task statuses (e.g., success, failure, pending) and button types, as well as persisting settings to the Host configuration. Additionally, it exposes the `ctx.uisfx` API for other DSH plugins to call for playing sounds, switching styles, or adjusting volume. Installation requires DSH 0.1.0-rc.6.