feat: expand test battery from 44 to 80 smoke tests

feat: expand test battery from 44 to 80 smoke tests

New init.elf tests (D1-D15):
- nanosleep (50ms sleep + monotonic clock verification)
- CLOCK_REALTIME (nonzero epoch timestamp)
- /dev/urandom read
- /proc/cmdline read
- CoW fork (child write doesn't corrupt parent)
- readv/writev (scatter-gather I/O on pipe)
- fsync (write + sync on diskfs)
- truncate (path-based length reduction)
- getuid/getgid/geteuid/getegid (identity consistency)
- chmod (mode change on diskfs file)
- flock (LOCK_EX + LOCK_UN)
- times (process accounting)
- gettid (== getpid for main thread)
- posix_spawn (fork+exec echo.elf)
- clock_ns precision (TSC sub-10ms resolution)

Newly tracked existing tests (~15):
- pipe rw, ioctl tty, job control, poll /dev/null, pty,
  setsid/setpgid, sigaction SIGUSR1, sigreturn, tmpfs/mount,
  /dev/null, isatty, O_NONBLOCK, pipe2/dup3, chdir/getcwd,
  *at syscalls, rename/rmdir, getdents multi-fs, getppid,
  waitpid WNOHANG, SIGSEGV handler, waitpid 100 children,
  echo.elf execve

Smoke timeout raised from 90s to 120s.
80/80 smoke tests pass, cppcheck clean.