fs rewrite stage 3: nested directories, paths, cwd (cd/mkdir/ls)

- directories generalized: dir_find/dir_add/dir_remove take any dir inode;
  every dir carries '.'/'..'. Path resolution (resolve / resolve_parent) walks
  absolute or cwd-relative paths; open/mkdir/chdir/remove/opendir take paths.
- per-process cwd: PROC_CWD in the PCB (root by default, inherited on fork);
  sys_chdir sets it, sys_opendir points ls at any directory.
- shell: 'cd' builtin + cwd-aware prompt; 'mkdir'/'ls <dir>' tools; 'exit'/'quit'
  and EOF call poweroff() (clean shutdown via the $ED opcode -> reliable save).
- three HL/buffer-clobber bugs fixed along the way: resolve didn't preserve the
  path cursor across dir_find; cur_cwd clobbered HL; resolve_parent set the final
  name before resolve() overwrote wFsNameBuf (now copied after).
- verified: nested mkdir/cd/save, multi-level paths (cat docs/sub/b), and the
  whole tree persists across a reboot.
- README: document directories + the poweroff opcode.

1 files changed, 4 insertions, 0 deletions

diff --git a/c/gbos.h b/c/gbos.h
index 6badd16..c93414f 100644
--- a/c/gbos.h
+++ b/c/gbos.h
@@ -27,6 +27,10 @@ int           fgetc(unsigned char fd);          /* a byte, or -1 at EOF */
 void          fputc(unsigned char fd, char ch);
 unsigned char flist(unsigned char slot, char *namebuf); /* 1 if slot used */
 void          fremove(const char *name);
+unsigned char mkdir(const char *path);
+unsigned char chdir(const char *path);
+unsigned char opendir(const char *path);
+void          poweroff(void);   /* clean emulator shutdown (saves) */
 #define O_READ  0
 #define O_WRITE 1
 #define NOFD    0xFF