Add support for Xcode tools MCP in Xcode 26.3

[cjheinze]

Xcode 26.3 adds an MCP for Xcode tools (launched via xcrun mcpbridge), for e.g. building, testing, rendering previews, etc. Unfortunately it does not follow the standard MCP scheme and returns "content" instead of "structuredContent". Right now I use it via a python script that converts it but it would be nice with native support for it.

[mobile-ar]

@cjheinze If you want to try I released https://github.com/mobile-ar/xcode-assistant-copilot-sever to proxy directly to support native Xcode Code Assistant features in 26.3. (Also works for all Xcode 26 versions)