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.

web/src/lib/CommandLine.svelte

@@ -28,7 +28,7 @@
 
 <script lang="ts">
   import { tick, untrack } from 'svelte'
-  import { argCompletions, completions, runCommand, hooks } from './commands'
+  import { argCompletions, completions, readingDocument, runCommand, hooks } from './commands'
   import { workspace } from './store.svelte'
 
   interface Props {
@@ -56,17 +56,16 @@
   /*
    * A capture line — `c` opens one — writes a thought down somewhere without
    * going there: a card, a note, a line in today's entry. Tab walks the three
-   * with the text kept. A card stays linked to the document being read when
-   * the line began as one that was.
+   * with the text kept. Reading a document, `:card` makes one about it.
    */
-  const card = untrack(() => (initial.startsWith(':card! ') ? 'card!' : 'card'))
-  const targets = [card, 'scratch', 'today']
-  const targetNames: Record<string, string> = { card: 'card', 'card!': 'card about this', scratch: 'note', today: 'today' }
-  const capture = $derived(/^:(card!?|scratch|today)\s/.exec(value)?.[1])
+  const about = untrack(readingDocument)
+  const targets = ['card', 'scratch', 'today']
+  const targetNames: Record<string, string> = { card: about ? 'card about this' : 'card', scratch: 'note', today: 'today' }
+  const capture = $derived(/^:(card|scratch|today)\s/.exec(value)?.[1])
 
   function retarget(delta: 1 | -1): boolean {
     if (!capture) return false
-    const at = targets.indexOf(capture === 'card!' || capture === 'card' ? card : capture)
+    const at = targets.indexOf(capture)
     const next = targets[(at + delta + targets.length) % targets.length]
     value = value.replace(/^:\S+/, `:${next}`)
     return true