docs(client): document bare gl/gL remove-checkbox + tick parity gap P1 #3

Update the lists keymap tables and group hints (gl/gL = remove checkbox;
remove-done is command-only via :NuwikiRemoveDone[!]), note the 'timeoutlen'
prefix behavior, and tick P1 #3 in the vimwiki gap tracker.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

doc/nuwiki.txt

@@ -456,8 +456,13 @@ Lists (normal mode) ~
              of `-` `*` `#` `1` (1.) `i` (i)) `I` (I)) `a` (a)) `A` (A)).
              For `1)` use `:NuwikiChangeSymbol 1)` (no single-key form).
   gL<sym>    Set every item in the list to <sym> (same symbol keys).
-  gl<Space>  Remove every completed item from the current list.
-  gL<Space>  Remove every completed item in the buffer.
+  gl         Remove the checkbox from the current item, keeping its text.
+  gL         Remove the checkbox from every item in the current list.
+             Bare `gl`/`gL` share the `gl...` prefix above, so (like
+             upstream vimwiki) they fire only after 'timeoutlen'; type a
+             suffix such as `gln`/`gl*` quickly to reach the prefixed maps.
+             Removing done items is command-only: `:NuwikiRemoveDone`
+             (current list) / `:NuwikiRemoveDone!` (whole buffer).
   o          Open a new line and continue the list marker (preserves
              any checkbox).
   O          Same, opening above the current line.