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>

development/tests/test-keymaps.lua

@@ -139,7 +139,7 @@ vim.defer_fn(function()
     'RebuildTags', '2HTML', '2HTMLBrowse', 'All2HTML', 'Rss',
     'NormalizeLink', 'RenumberList', 'RenumberAllLists',
     'ListToggle', 'IncrementListItem', 'DecrementListItem',
-    'CatUrl',
+    'CatUrl', 'ShowVersion',
   }
   for _, suffix in ipairs(both_forms) do
     for _, prefix in ipairs({ 'Nuwiki', 'Vimwiki' }) do
@@ -212,6 +212,8 @@ vim.defer_fn(function()
     { '<C-Space>', 'nx' }, { '<C-@>', 'nx' }, { '<Nul>', 'nx' },
     { 'gnt', 'n' }, { 'gln', 'nx' }, { 'glp', 'nx' }, { 'glx', 'nx' },
     { 'glh', 'n' }, { 'gll', 'n' }, { 'gLh', 'n' }, { 'gLl', 'n' },
+    -- Upstream case-variant aliases of gLh/gLl/gLr.
+    { 'gLH', 'n' }, { 'gLL', 'n' }, { 'gLR', 'n' },
     { 'glr', 'n' }, { 'gLr', 'n' }, { 'gl', 'n' }, { 'gL', 'n' },
     { 'gl-', 'n' }, { 'gL-', 'n' }, { 'gl*', 'n' }, { 'gL*', 'n' },
     { 'gl#', 'n' }, { 'gL#', 'n' }, { 'gl1', 'n' }, { 'gL1', 'n' },