Add redbear-usb-storage-check in-guest binary that validates USB mass
storage read and write I/O: discovers /scheme/disk/ devices, writes a
test pattern to sector 2048, reads it back, verifies match, restores
original content. Updates test-usb-storage-qemu.sh with write-proof
verification step.
Includes all accumulated Red Bear OS work: kernel patches, relibc
patches, driver infrastructure, DRM/GPU, KDE recipes, firmware,
validation tooling, build system hardening, and documentation.
relibc select_epoll() forced timeout=0 when any FD doesn't support epoll
(e.g. TTY on Redox), causing busy-loop. Poll with 100ms interval instead.
Also add stdint.h to signal/cbindgen.toml sys_includes so signalfd_siginfo
struct types (uint32_t, int32_t) resolve without build errors.