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>

docs/vault.1

@@ -37,8 +37,10 @@ Crawl a website into the vault.
 Add every file in a tar archive read from standard input.
 .TP
 .BR vault\-list (1)
-List stored files (alias:
-.BR ls ).
+.B ls
+lists one folder, with sub-folders marked;
+.B list
+lists every file under a folder.
 .TP
 .BR vault\-get (1)
 Decrypt a stored file.
@@ -48,7 +50,9 @@ Rename a stored file (alias:
 .BR rename ).
 .TP
 .BR vault\-rm (1)
-Delete a stored file (alias:
+Delete a stored file, or a whole folder with
+.B \-r
+(alias:
 .BR delete ).
 .TP
 .B help