Userspace malloc, WM overhaul, framebuffer pixel format support
* Implement userspace malloc backed by mmap arenas with realloc,
replace static buffers with dynamic allocation across userspace
* Use vector for WM window storage, add wallpaper support with
PPM parser and /etc/wm.conf
* Proper pixel format handling (shift+size) in console, present
path, and boot (UEFI GOP + VESA channel layout)
* Fix terminal deferred line wrap breaking vi cursor positioning
* Fix mmap base selection skipping COW-split stack regions