Add Apple environment check API (`maui apple check`)

[rmarinho]

Summary

Add library APIs to check the Apple development environment status, supporting the maui apple check command from the CLI spec.

Requirements

The check should detect and report:

• Xcode version(s) installed and which is active (xcode-select -p)
• Command Line Tools (CLT) presence and version
• Installed simulator runtimes (iOS, tvOS, watchOS, visionOS)
• Enabled platform support (Xcode 16+ platform management)
• Whether the environment is sufficient for .NET MAUI development

Expected Output

The API should return a structured result that can be serialized to JSON:

{
  "xcode": { "version": "16.2", "path": "/Applications/Xcode.app", "build": "16C5032a" },
  "clt": { "installed": true, "version": "16.2.0" },
  "runtimes": [ { "platform": "iOS", "version": "18.2", "identifier": "com.apple.CoreSimulator.SimRuntime.iOS-18-2" } ],
  "platforms": [ "iOS", "macOS" ],
  "status": "ok"
}

Design Notes

• Leverages the existing XcodeLocator class for Xcode discovery
• Should be stateless — reads system state and returns results
• Must work on macOS only (return appropriate error on other platforms)

Reference

• CLI spec PR
• Full specification