commands: one grammar for !, merged commands, a settings sheet, two-level help

A `!` now means force or everything and nothing else (`:w!`, `:search!`,
`:export!`, `:logout!`). A command that did a second thing behind its bang
takes a word for it instead: `:space new|name|rm`, `:list name|rm`,
`:task [add]|edit`, `:upload seal`, `:import zip [/]`. `:card` while reading
a document makes a card about it, so `:card!` is gone.

Merged: `:export` downloads what has focus, a file as it is or a document as
markdown (`:download` folded in); `:share [off|new]` replaces `:unshare` and
`:link`, and the list's `s` and `y` give way to it and the info sheet;
`:noh` replaces `:clear`; `:vault [unlock|lock|passwd]` replaces `:unlock`,
`:lock` and `:passwd`; Esc in the list puts down what `m` picked up before it
closes the document, replacing `:unmark`.

The old spellings run as their new lines for one release through a table in
commands.ts; help and Tab leave them out, and the wiki lists them.

A settings sheet (`,` or `:settings`) holds the options, the vault, the
backup, the signed-in browsers, ssh keys and capture tokens. Each row runs
the command a line would. Bare `:set`, `:vault`, `:backup`, `:sessions`,
`:sshkey` and `:token` open it at their part.

`?` shows the keys and commands to start with, flagged in the keymap and the
command table; a second `?` (or `:help all`) shows all of them, and a filter
always searches all of them. Help rows are keyed by key and description, as
two contexts can share a label.

docs/wiki/Boards-and-Agenda.md

@@ -51,8 +51,8 @@ something by where they stand, not by their names:
   list: moving it there stamps it, moving it out reopens it;
 - the lists between are **work in hand**, which the agenda shows.
 
-`:list <name>` adds a list in front of the last one, `:name!` renames the list
-under the cursor, and `:list!` deletes it with its cards. Done cards older than
+`:list <name>` adds a list in front of the last one, `:list name` renames the list
+under the cursor, and `:list rm` deletes it with its cards. Done cards older than
 a week fold away until `z` shows them.
 
 | key | what it does |
@@ -84,7 +84,7 @@ as they do on the board.
 | `j` / `k`, `gg` / `G` | down / up the checklist, its first / last step |
 | `Space`, `x` | tick the step, or untick it |
 | `o` | a new step below the cursor (`:task <text>`) |
-| `r` | reword the step (`:task! <text>`) |
+| `r` | reword the step (`:task edit <text>`) |
 | `J` / `K` | move the step down / up |
 | `dd` | drop the step |
 | `e`, `i`, `Enter` | write the description |
@@ -112,8 +112,8 @@ step open again.
 
 `c` in the tree opens `:card ` on the command line. The card goes
 into the inbox of the space you are in, or of the first space with a board, and
-you stay where you were. Reading a document, `c` opens `:card! ` instead: the
-card is about that document, and an empty title takes the document's. From
+you stay where you were. Reading a document, `:card` makes the card about that
+document, and an empty title takes the document's. From
 outside the browser, see [Capture](Capture.md).
 
 ### Notes