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/keymaps.lua

@@ -225,10 +225,17 @@ function M.attach(bufnr, mappings)
         { desc = 'nuwiki: list dedent subtree' }, bufnr)
     map('n', 'gLl', function() cmd.list_change_level(1, true) end,
         { desc = 'nuwiki: list indent subtree' }, bufnr)
+    -- Upstream binds case-variant aliases gLH/gLL/gLR == gLh/gLl/gLr.
+    map('n', 'gLH', function() cmd.list_change_level(-1, true) end,
+        { desc = 'nuwiki: list dedent subtree' }, bufnr)
+    map('n', 'gLL', function() cmd.list_change_level(1, true) end,
+        { desc = 'nuwiki: list indent subtree' }, bufnr)
     map('n', 'glr', cmd.list_renumber,
         { desc = 'nuwiki: renumber list' }, bufnr)
     map('n', 'gLr', cmd.list_renumber_all,
         { desc = 'nuwiki: renumber all lists' }, bufnr)
+    map('n', 'gLR', cmd.list_renumber_all,
+        { desc = 'nuwiki: renumber all lists' }, bufnr)
     -- gl<sym>/gL<sym>: set the current item's / whole list's marker (upstream
     -- VimwikiChangeSymbolTo / ChangeSymbolInListTo). 1) is command-only.
     for _, pair in ipairs({