Headless.cpp, NativeApp.cpp, and SDLMain.cpp each still hand-parsed a few
argv flags directly (mount/log/state/ignore/loglevel in headless and the
app, xres/yres/dpi/scale in SDL), duplicating and in some cases conflicting
with the shared CommandLineOptions parser. Consolidate all of it into
CmdLine.cpp/.h so there's a single source of truth, and drop the now-dead
remain_argc/remain_argv filtering in SDLMain.cpp since NativeInit no longer
reads argv itself.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PfFvWzpHxErWgRhKqqSewN
