Add rm -r for folders, and make ls list one folder level

rm -r FOLDER deletes a folder and everything under it, records and
objects, so the space is freed. It lists what will go (the first 20
names, then a count) with the total size and asks on the terminal; no
answer or no terminal deletes nothing. -f skips the question and makes a
missing name a no-op, -rf and -fr combine them, and rm -r / is refused.
Objects still in use are worked out once per delete, not once per file.

ls now shows one level, like ls(1): sub-folders once with a trailing
slash, their total size and newest date, then the files, with names
relative to the folder. list keeps the recursive listing of full names
that scripts pipe through cut -c31-, and ls -r is the same.

Docs, man pages, the guide (new rm-r screenshot) and README follow.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CLAUDE.md

@@ -9,7 +9,8 @@ root that builds a single `vault` binary. Module `github.com/andydixon/vault`.
 
 - `main.go` - CLI: `genkey`, `init`, `add` (file, directory
   or URL), `migrate` (add, then delete originals), `mirror`, `absorb` (tar
-  on stdin, `absorb.go`), `list`, `get`, `mv`, `rm`.
+  on stdin, `absorb.go`), `ls` (one folder level), `list` (recursive),
+  `get`, `mv`, `rm` (`-r` for a folder, asks unless `-f`).
 - `keyfile.go` - key file with two passphrase slots (Argon2id +
   XChaCha20-Poly1305 sealing a suite ID and 32-byte master seed). The second
   slot is either a decoy identity or random bytes; slot order is random.