feat(parity): close the entire P3 Commands section

All six remaining command gaps (client-side; no server change):

- VimwikiRenameFile: bare -> -nargs=? (arg accepted-ignored; rename still
  delegates to the LSP rename prompt). No more E488.

- VimwikiVar / NuwikiVar: get/set the client config (upstream vimwiki#vars#cmd).
  No arg prints config (Vim: g:nuwiki_*; Neovim: resolved setup() opts), one arg
  gets a key, two+ sets it. Global command, both clients.

- VimwikiReturn / NuwikiReturn: command form of the smart <CR> continuation —
  enters insert at EOL and fires the <CR> mapping (return_cmd / vimwiki_return).
  Upstream's mode-flag args accepted but unused.

- VimwikiTableAlignQ vs AlignW: corrected — upstream's gqq/gww are identical on
  a table; the only difference is the non-table fallback (native `normal! gqq`
  vs `gww`). New table_align_or_cmd(cmd) aligns on a table row, else runs
  `normal! <cmd>`. Q/gqq/gq1 -> gqq; W/gww/gw1 -> gww; NuwikiTableAlign -> gqq.

- VimwikiSearch / VWS: scope the lvimgrep to the current wiki's root (resolved
  client-side) over <root>/**/*<ext>, not CWD `**`; empty pattern reuses the
  last search. Both clients.

- VimwikiIndex family: add global Vimwiki/NuwikiIndex + TabIndex entry points
  (plugin/nuwiki.vim + init.lua _setup_global_commands, with -count), so a wiki
  opens from any buffer. Buffer-local copies still shadow inside wiki buffers.

Tests: surface.{Vimwiki,Nuwiki}{Return,Var}, cmd.VimwikiVar_sets_*,
cmd.global_entry_points (both harnesses). Docs (README + doc/nuwiki.txt) and the
gap doc updated. Neovim 299, Vim 291/18/21 pass.

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

lua/nuwiki/keymaps.lua

@@ -303,10 +303,10 @@ function M.attach(bufnr, mappings)
 
   -- ===== Tables =====
   if on('table_editing') then
-    map('n', 'gqq', cmd.table_align, { desc = 'nuwiki: align table' }, bufnr)
-    map('n', 'gq1', cmd.table_align, { desc = 'nuwiki: align table' }, bufnr)
-    map('n', 'gww', cmd.table_align, { desc = 'nuwiki: align table (wide)' }, bufnr)
-    map('n', 'gw1', cmd.table_align, { desc = 'nuwiki: align table (wide)' }, bufnr)
+    map('n', 'gqq', function() cmd.table_align_or_cmd('gqq') end, { desc = 'nuwiki: align table / gqq' }, bufnr)
+    map('n', 'gq1', function() cmd.table_align_or_cmd('gqq') end, { desc = 'nuwiki: align table / gqq' }, bufnr)
+    map('n', 'gww', function() cmd.table_align_or_cmd('gww') end, { desc = 'nuwiki: align table / gww' }, bufnr)
+    map('n', 'gw1', function() cmd.table_align_or_cmd('gww') end, { desc = 'nuwiki: align table / gww' }, bufnr)
     map('n', '<A-Left>',  cmd.table_move_column_left,  { desc = 'nuwiki: move column left' }, bufnr)
     map('n', '<A-Right>', cmd.table_move_column_right, { desc = 'nuwiki: move column right' }, bufnr)
   end