2026-09-01 (freestanding headers) - removed <sys/types.h> from injector headers and defined freestanding types

Fixed freestanding cross-compilation failure under -nostdlib / HARDWARE=1:

• src/common/freestd.h: Defined freestanding pid_t, off_t, and ssize_t types guarded by _PID_T_DECLARED, _OFF_T_DECLARED, _SSIZE_T_DECLARED.
• src/common/krw.h, src/injector/procctl.h, src/injector/target.h, src/injector/loader.h: Replaced #include <sys/types.h> with #include "common/freestd.h".
• src/injector/injector.c: Added /data/obscene-payload.elf to fallback search path.

Verified: make payload injector HARDWARE=1 and ./bin/obscene inject --build-only compile 100% clean with zero warnings or errors. bash scripts/verify.sh green.