dsh-mcp-xcode: Integrate Xcode headless capabilities into DSH agent

# Introduction When developing macOS/iOS applications in DSH (DeepSeek Harness), there is a practical challenge: tasks such as building projects, running unit tests, viewing SwiftUI previews, and operating simulators are typically performed within the Xcode UI, preventing agents from intervening. DSH's philosophy is "everything is a plugin," and such capability gaps are usually filled by plugins. Starting with Xcode 27, the system comes with built-in headless MCP services (`xcrun mcp-server` / `xcrun mcpbridge`) that expose the aforementioned capabilities in the form of MCP tools. However, to use them within DSH, a bridging layer is required to convert these MCP tools into...