feat(commands): VimwikiTable -nargs=* + Index/TabIndex -count=0 (P3 parity)

Two command-attribute parity fixes (audited against upstream vimwiki master):

- VimwikiTable / NuwikiTable were -nargs=1 and called table_insert() with no
  args, so `:VimwikiTable 4 3` raised E488 and cols/rows were unreachable.
  All four defs (Vim+Neovim × Vimwiki+Nuwiki) are now -nargs=* and forward
  <f-args>; the backing table_insert already parsed cols (a:1) + rows (a:2).

- VimwikiIndex/TabIndex (and Nuwiki forms) switch from bare -count to
  upstream's -count=0. Behavior is unchanged (both default count to 0;
  wiki_index already maps a count to the 1-indexed wiki number) — this just
  matches the upstream declaration exactly.

Tests: cmd.VimwikiTable_passes_cols_and_rows (test-keymaps.lua — asserts a
4-col/3-row table) and cmd.VimwikiTable_accepts_cols_rows (test-keymaps-vim.vim
— no E488). gap doc updated.

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

.claude/scheduled_tasks.lock

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