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>

lua/nuwiki/commands.lua

@@ -276,6 +276,15 @@ end
 -- Pick a wiki and open its index. The list is read straight from config
 -- (no LSP round-trip) so this works from any buffer before a wiki file is
 -- ever opened; opening the index then auto-starts the server.
+-- :VimwikiShowVersion / :NuwikiShowVersion — echo the nuwiki version + editor.
+function M.show_version()
+  local ver = vim.g.nuwiki_version or '?'
+  vim.api.nvim_echo({
+    { 'nuwiki: ' .. ver .. '\n' },
+    { 'Neovim: ' .. tostring(vim.version()) },
+  }, false, {})
+end
+
 function M.wiki_ui_select()
   local wikis = require('nuwiki.config').wiki_list()
   if #wikis == 0 then