Add a new `Process.cwd` static method that retrieves the current working directory via libuv's `uv_cwd` function. The implementation includes proper error handling that aborts the fiber with a descriptive message on failure. The foreign method is registered in the module table and exposed in the Wren API with a foreign static declaration. A test suite validates that the returned value is a non-empty string starting with "/", resolves correctly via `File.realPath`, and corresponds to an existing directory.
Rename the "process" module to "os" across all source files, documentation, tests, and build configuration. Add a new Platform class to the os module with static methods `name` (returns OS string like "Windows", "Linux", "OS X", "iOS", "Unix", "POSIX", or "Unknown") and `isPosix` (returns bool indicating POSIX compliance). Update all import paths from "process" to "os" in test files and module registrations. Move process.c/h to os.c/h, rename processSetArguments to osSetArguments, and regenerate the os.wren.inc bytecode source. Add documentation pages for the os module and Platform class.
