fix(parity): fifth-pass re-audit — VimwikiGoto nargs, autowriteall, table_auto_fmt

Closes the actionable fifth-pass findings (gap doc updated):

- VimwikiGoto / NuwikiGoto: -nargs=1 -> -nargs=* in all four defs. Was a
  real bug — `:VimwikiGoto` raised E471, `:VimwikiGoto My Page` raised E488,
  and the handler's empty-arg prompt fallback was unreachable. Both clients
  already prompt on empty, so -nargs=* (keeping -complete=pages) restores
  upstream behavior.

- autowriteall (upstream default ON): while a wiki buffer is current, mirror
  Vim's global 'autowriteall' (auto-save on page switch / :make), restoring
  the prior value on leave. Neovim via ftplugin.lua setup_autowriteall
  (BufEnter/BufLeave) gated by the `autowriteall` setup option; Vim via the
  NuwikiAutoWriteAll augroup gated by g:nuwiki_autowriteall.

- table_auto_fmt (upstream default ON): re-align the table under the cursor
  on InsertLeave. Both clients, gated by `table_auto_fmt` / g:nuwiki_table_auto_fmt,
  guarded on the cursor line containing `|` before the async table_align.

Also logged (no code): VimwikiRenameFile missing -nargs=? (subsumed by the
LSP-rename divergence), table_reduce_last_col, user_htmls, hl_headers/
hl_cb_checked, and a commentstring value-mismatch note. Mappings audit clean.

The Neovim harness disables table_auto_fmt in setup (its async re-align would
perturb the deterministic table-nav keystroke cases); its wiring is verified
on a throwaway scratch buffer instead. Docs (README + doc/nuwiki.txt) updated.
Tests: cmd.VimwikiGoto_accepts_multiword, config.autowriteall_applied,
config.table_auto_fmt_autocmd. Neovim 293, Vim 285/18/21 pass.

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

doc/nuwiki.txt

@@ -306,6 +306,20 @@ Vim-specific globals ~
 `g:nuwiki_no_folding`          0
     When 1, the Vim path skips `foldexpr` / `foldmethod` setup.
 
+                                                       *g:nuwiki_autowriteall*
+`g:nuwiki_autowriteall`        1
+    When 1 (default), Vim's global `'autowriteall'` is set while a wiki
+    buffer is current and restored on leave, so a modified buffer is
+    auto-saved on page switch / `:make`. Mirrors vimwiki's `autowriteall`
+    and the Neovim `autowriteall` setup option. Set to 0 to leave
+    `'autowriteall'` untouched.
+
+                                                     *g:nuwiki_table_auto_fmt*
+`g:nuwiki_table_auto_fmt`      1
+    When 1 (default), the table under the cursor is re-aligned on
+    |InsertLeave|. Mirrors vimwiki's `table_auto_fmt` and the Neovim
+    `table_auto_fmt` setup option. Set to 0 to disable.
+
                                                      *g:nuwiki_mouse_mappings*
 `g:nuwiki_mouse_mappings`      0
     When 1, the Vim path registers mouse keymaps (double-click follows,