fix(client): VimwikiColorize passes its {color} arg on Neovim + visual fix

The Neovim command defs for :VimwikiColorize / :NuwikiColorize were
-nargs=1 but called colorize() without <q-args>, so the colour name was
silently dropped and the user was prompted instead (the Vim branch passed
it correctly). Pass <q-args>.

While verifying, found a second bug in the Lua colorize(): it inferred
visual-vs-normal from vim.fn.visualmode(), which returns the *last* visual
mode used in the session along with stale '< / '> marks. So running
:VimwikiColorize in normal mode after any earlier visual selection wrapped
that leftover selection instead of the word under the cursor (produced an
empty, misplaced span). colorize(color, visual) now takes an explicit
visual flag, passed only by the x-mode <Leader>wc mapping; the command and
the normal-mode mapping always wrap the cword.

Tests: cmd.VimwikiColorize_uses_arg, cmd.NuwikiColorize_uses_arg,
cmd.Colorize_ignores_stale_visual_selection, colorize.visual_wraps_selection
in test-keymaps.lua. nvim suite 267, vim suite 254+18, all green.

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

ftplugin/vimwiki.vim

@@ -442,7 +442,7 @@ command! -buffer -nargs=? VimwikiGenerateTags      lua require('nuwiki.commands'
 command! -buffer -nargs=1 VimwikiTable             lua require('nuwiki.commands').table_insert()
 command! -buffer        VimwikiTableMoveColumnLeft  lua require('nuwiki.commands').table_move_column_left()
 command! -buffer        VimwikiTableMoveColumnRight lua require('nuwiki.commands').table_move_column_right()
-command! -buffer -nargs=1 VimwikiColorize          lua require('nuwiki.commands').colorize()
+command! -buffer -nargs=1 VimwikiColorize          lua require('nuwiki.commands').colorize(<q-args>)
 command! -buffer        VimwikiPasteLink           lua require('nuwiki.commands').paste_link()
 command! -buffer        VimwikiPasteUrl            lua require('nuwiki.commands').paste_url()
 command! -buffer        VimwikiCatUrl              lua require('nuwiki.commands').cat_url()
@@ -514,7 +514,7 @@ command! -buffer        NuwikiTableAlign             lua require('nuwiki.command
 command! -buffer -nargs=1 NuwikiTable               lua require('nuwiki.commands').table_insert()
 command! -buffer        NuwikiTableMoveColumnLeft    lua require('nuwiki.commands').table_move_column_left()
 command! -buffer        NuwikiTableMoveColumnRight   lua require('nuwiki.commands').table_move_column_right()
-command! -buffer -nargs=1 NuwikiColorize            lua require('nuwiki.commands').colorize()
+command! -buffer -nargs=1 NuwikiColorize            lua require('nuwiki.commands').colorize(<q-args>)
 command! -buffer        NuwikiPasteLink              lua require('nuwiki.commands').paste_link()
 command! -buffer        NuwikiPasteUrl               lua require('nuwiki.commands').paste_url()
 command! -buffer        NuwikiCatUrl                 lua require('nuwiki.commands').cat_url()