Add MCP screenshots for Compose dev tools

[alexstyl]

What changed

• Added a devtools automation HTTP server that exposes readiness and direct preview-buffer screenshots.
• Added a runDevToolsMcpServer Gradle task that exposes status and take_screenshot MCP tools.
• Wired generated devtools hosts to start the automation server and run Compose Hot Reload devtools headless.
• Added local Maven publishing metadata for the devtools modules so consuming repos can use the local plugin/runtime.

Why

This lets automation inspect the Composables Dev Tools preview directly without relying on macOS window screenshots, which can capture the wrong top-level window.

Validation

• ./gradlew --console=plain test
• ./gradlew --console=plain spotlessCheck