Replace the non-portable PATH_MAX constant with a new WREN_PATH_MAX define set to 4096 in os.h, and correct the void function processCwd to use bare return instead of return wrenAbortFiber(vm, 0) which was causing a broken build on platforms without PATH_MAX defined.
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.
