fix(tables): cycle Tab into the next row instead of inserting one

Pressing <Tab> past the last cell unconditionally appended a new row
below, even when there was already a next row to jump into. Tabbing
through a header → separator → body table from the header row
inserted a blank row between header and separator instead of landing
in the first body cell.

After the final cell, walk forward from the current row to the end
of the table, skip any separator row, and jump to the first cell of
the next data row. Only insert a fresh row when the cursor is on the
table's last row (or only separator rows follow). Applied to both
the Vim (autoload/nuwiki/commands.vim) and Neovim (lua/nuwiki/
commands.lua) sides so the two harnesses stay in sync; covered by
new keymap tests in scripts/test-keymaps-vim.vim and test-keymaps.lua.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

autoload/nuwiki/commands.vim

@@ -1025,10 +1025,22 @@ function! nuwiki#commands#smart_tab() abort
   if l:target_idx < len(l:starts)
     return "\<Cmd>call nuwiki#commands#_table_jump_to_cell(" . line('.') . ", " . l:target_idx . ")\<CR>"
   endif
-  " Past the final cell → add a fresh row below, cursor in its first cell.
+  " Past the final cell. Prefer cycling into the next existing row (skipping
+  " any separator row); only insert a fresh row when we're already on the
+  " table's last row.
+  let l:row = line('.')
+  let [l:s_row, l:e_row] = s:find_table_range(l:row)
+  let l:next = l:row + 1
+  while l:next <= l:e_row
+    let [l:_, l:next_cells] = s:parse_table_row(getline(l:next))
+    if !s:is_sep_row(l:next_cells)
+      return "\<Cmd>call nuwiki#commands#_table_jump_to_cell(" . l:next . ", 1)\<CR>"
+    endif
+    let l:next += 1
+  endwhile
   let l:indent = matchstr(l:line, '^\s*')
   let l:cursor_col = len(l:indent) + 2
-  return "\<Cmd>call nuwiki#commands#_table_insert_row_below(" . line('.') . ", " . l:cursor_col . ")\<CR>"
+  return "\<Cmd>call nuwiki#commands#_table_insert_row_below(" . l:row . ", " . l:cursor_col . ")\<CR>"
 endfunction
 
 function! nuwiki#commands#smart_shift_tab() abort