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, 1 deletions

diff --git a/c/ls.c b/c/ls.c
index 5d5ce43..0e2e01f 100644
--- a/c/ls.c
+++ b/c/ls.c
@@ -1,7 +1,10 @@
 #include "gbos.h"
-/* ls: list files in the filesystem. */
+/* ls [dir]: list a directory (default: current). */
 void main(void) {
+    char *argv[4];
     char name[16];
+    unsigned char argc = argv_parse(argv, 4);
     unsigned char i;
+    if (opendir(argc > 0 ? argv[0] : ".")) { puts("ls: no such directory"); nl(); return; }
     for (i = 0; flist(i, name); i++) { name[15] = 0; puts(name); nl(); }
 }