feat: add Claude plugin browser URL config

[officialasishkumar]

Summary

• add a Claude plugin browserUrl user config option for connecting to a running debuggable Chrome instance
• pass the option through to chrome-devtools-mcp with --browser-url, while a blank value keeps the default automatic Chrome launch behavior
• document the Claude Code pluginConfigs settings shape for the plugin option

Fixes #1232

Testing

• parsed .claude-plugin/plugin.json with JSON.parse
• npm run check-format
• npm run gen