Add Windows support and named-pipe broker

Add Windows support across CLI, broker, native host, and plugin by using a platform-aware broker socket (Unix socket or Windows named pipe) and safe pipe naming. Implement OPENCODE_BROWSER_BROKER_SOCKET override, create host-wrapper.cmd on Windows, and add registry registration/unregistration and status checks for Chrome/Edge/Brave/Chromium native messaging hosts. Improve plugin diagnostics and logging (plugin.log), include broker socket info in debug/status output, and enhance broker connection errors with underlying messages. Also update README to list supported OSes. Files changed: bin/cli.js, bin/broker.cjs, bin/native-host.cjs, src/plugin.ts, dist/plugin.js, README.md.