feat(parity): P3 quick-wins — ShowVersion, gLH/gLL/gLR, Search/Align nargs

Closes four low-risk P3 parity items (gap doc updated):

- VimwikiShowVersion / NuwikiShowVersion: new global command (both clients)
  echoing g:nuwiki_version (0.1.0) + the host editor, via
  nuwiki#commands#show_version / commands.show_version.

- gLH / gLL / gLR: upstream's case-variant aliases of gLh/gLl/gLr (dedent /
  indent whole item, renumber all lists) added in both clients.

- VimwikiSearch / VWS: -nargs=1 -> -nargs=* (Vim + Neovim), so a multi-word
  search no longer raises E488 and an empty invocation reuses the last search
  pattern. (The lvimgrep-vs-vimwiki-engine difference stays open.)

- VimwikiTableAlignQ / AlignW / NuwikiTableAlign: bare -> -nargs=?, so
  `:VimwikiTableAlignQ 2` no longer raises E488 (optional column arg is
  accepted-and-ignored; the gqq-align vs gww-align-without-resize split
  stays open).

Docs (doc/nuwiki.txt + README) updated for the command and the aliases.
Tests: surface.{Vimwiki,Nuwiki}ShowVersion, map[n].gL{H,L,R} (both
harnesses), cmd.search_and_tablealign_nargs (vim). Neovim 291, Vim
282/18/21 pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

plugin/nuwiki.vim

@@ -12,6 +12,12 @@ if exists('g:loaded_nuwiki')
 endif
 let g:loaded_nuwiki = 1
 
+" Plugin version, surfaced by :VimwikiShowVersion / :NuwikiShowVersion.
+" Set before the Neovim early-return below so both clients see the global.
+if !exists('g:nuwiki_version')
+  let g:nuwiki_version = '0.1.0'
+endif
+
 " Resolve the plugin root NOW, while this script is being sourced and
 " <sfile> is still valid. Commands that need this path must reference
 " s:plugin_root — re-expanding <sfile> inside a command body evaluates
@@ -47,6 +53,10 @@ augroup END
 command! -nargs=0 VimwikiUISelect call nuwiki#commands#wiki_ui_select()
 command! -nargs=0 NuwikiUISelect  call nuwiki#commands#wiki_ui_select()
 
+" Print the nuwiki version + host editor (upstream's :VimwikiShowVersion).
+command! -nargs=0 VimwikiShowVersion call nuwiki#commands#show_version()
+command! -nargs=0 NuwikiShowVersion  call nuwiki#commands#show_version()
+
 " Global entry-point mappings — work from any buffer, not just .wiki files.
 " Files are opened directly from config (no LSP required); the server
 " auto-starts via the FileType autocmd once the vimwiki buffer loads.