keys: the command line remembers and completes

`↑` / `↓` (and `Ctrl-p` / `Ctrl-n`) walk the lines run before, newest
first, narrowed by what is already typed: `:se` then `↑` finds the last
`:set …`. Commands and `/` searches keep separate histories in
localStorage, a hundred lines each. Passwords never get here: they are
typed into the vault prompt, not the line.

Tab moves to the next match and Shift-Tab to the one before, with the match
marked in the list. Once a name is complete, Tab completes the argument:
the folders listed here plus `..` and `/` for `:cd` and `:mv`, space names
for `:space` and `:rmspace`, the options of `:set`, `:due`'s usual dates and
`:backup`'s subcommands. `:mv /` now moves to the root of the space, as
`:cd /` goes there.

While a search is live, `Ctrl-n` / `Ctrl-p` (and Tab) move the list cursor
through the results without leaving the line, and Enter opens the one lit
rather than only closing the line. Ctrl-P's search does the same.

After a command the focus goes back where it was, or to the editor while
writing, instead of being left on <body> for the window handler to catch.

README.md

@@ -94,11 +94,11 @@ it; in the document pane it is that document. In the browse pane:
 | `c` | capture a card into this space's inbox without leaving where you are |
 | `Esc`, `q` | close the document |
 | `h` | up one level in the tree |
-| `/` | full-text search in this space (`n` clears it) |
+| `/` | full-text search in this space (`n` clears it); `Tab` or `Ctrl-N`/`Ctrl-P` walk the results without leaving the line, `Enter` opens the one lit |
 | `Ctrl-P` | full-text search across every space; `Enter` goes to the match |
 | `s` / `y` | toggle sharing / mint a new share link — either asks first when it would cut readers off |
 | `x`, `dd` | delete the entry under the cursor (asks `y`/`N`) |
-| `:` | command line |
+| `:` | command line — `Tab` / `Shift-Tab` cycle the matching commands, then the argument (folders for `:cd` and `:mv`, spaces for `:space`, options for `:set` …); `↑` / `↓` recall the lines run before that start as this one does |
 | `Ctrl-S` | save from anywhere |
 | `?` | help |
 
@@ -117,7 +117,7 @@ and lines, `:search!` searches every space, `:set clipboard` / `:set
 noclipboard` mirrors vim yanks to the system clipboard, `:logout` ends the
 session, `:logout!` every session and `:sessions rm <n>` one other. The tree has its own: `:space [name]` switches (`:space! <name>`
 makes one, `:rmspace [name]` deletes one and everything in it), `:mkdir <name>`
-makes a folder, `:cd <name|..|/>` walks it and `:mv <folder|..>` moves what is
+makes a folder, `:cd <name|..|/>` walks it and `:mv <folder|..|/>` moves what is
 selected, and `:import` uploads a folder into the one being browsed
 (`:import!` takes a `.zip` instead). `:upload` outside the editor puts files
 into the folder being browsed, and so does dropping them on the list. `:name <text>` renames whatever is under