keys act on the focused pane, deletes ask y/N in place

dd, x, i, R, s, y and :mv used the open document whenever one was open,
so walking the list and pressing dd deleted the document beside it. They
now act on the row under the cursor while the list has focus. Deletes ask
an in-app y/N naming the node instead of confirm(), and the board no
longer lets tree keys through to the hidden list.

README.md

@@ -49,7 +49,9 @@ works once the frontend has been built at least once.
 
 ## Keys
 
-The desktop UI is modal. In the browse pane:
+The desktop UI is modal, and a key acts on whatever has focus: in the list
+that is the row under the cursor, even while another document is open beside
+it; in the document pane it is that document. In the browse pane:
 
 | key | action |
 | --- | --- |
@@ -65,7 +67,7 @@ The desktop UI is modal. In the browse pane:
 | `h` | up one level in the tree |
 | `/` | full-text search (`n` clears it) |
 | `s` / `y` | toggle sharing / mint a new share link |
-| `x`, `dd` | delete the entry |
+| `x`, `dd` | delete the entry under the cursor (asks `y`/`N`) |
 | `:` | command line |
 | `Ctrl-S` | save from anywhere |
 | `?` | help |