Add missing :Nuwiki* aliases and drop dead deferred-stub code

Every :Vimwiki* command now has a canonical :Nuwiki* counterpart
(tables, colorize, clipboard paste, list-level/remove-done, and the
Neovim-only split/tab link-follow variants). Remove the now-unused
"not yet implemented" stub helpers (_not_yet, deferred,
s:notify_deferred) and the stale "deferred" comments, since every
command is implemented and server-backed.

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

autoload/nuwiki/commands.vim

@@ -105,12 +105,6 @@ function! s:open_uri_from(response, ...) abort
   execute l:cmd . ' ' . fnameescape(l:path)
 endfunction
 
-function! s:notify_deferred(name) abort
-  echohl WarningMsg
-  echom 'nuwiki: ' . a:name . ' is not yet implemented'
-  echohl None
-endfunction
-
 " ===== Wiki picker =====
 
 function! nuwiki#commands#wiki_index(count) abort
@@ -634,7 +628,7 @@ function! nuwiki#commands#rename_file() abort
   endif
 endfunction
 
-" ===== Deferred =====
+" ===== List, table & clipboard commands =====
 
 " Cluster A — list rewriters.