fix(wiki): build wiki picker list from config so it works before opening a file

The picker fetched the wiki list via workspace/executeCommand, but the LSP
only starts once a vimwiki buffer exists — so a wiki could not be selected
until one was already open (chicken-and-egg). Read the list straight from
config instead (g:nuwiki_wikis / scalar fallback, the same source as
open_wiki_path) and open the chosen index directly; that auto-starts the
server via the FileType autocmd.

- Vim: new public nuwiki#commands#wiki_list(); wiki_ui_select() uses it +
  inputlist() + :edit. Global :VimwikiUISelect / :NuwikiUISelect commands.
- Neovim: config.wiki_cfg(n) + config.wiki_list() (init.lua delegates);
  commands.wiki_ui_select() uses them + vim.ui.select + :edit; global
  VimwikiUISelect / NuwikiUISelect user commands registered in setup().

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

plugin/nuwiki.vim

@@ -39,6 +39,14 @@ augroup nuwiki_vim_lsp_start
   autocmd FileType vimwiki call nuwiki#lsp#start()
 augroup END
 
+" Global wiki-picker commands — available from any buffer so a wiki can be
+" chosen before a .wiki file exists. The picker reads its list from config
+" (no LSP); opening the chosen index then auto-starts the server. The
+" buffer-local :VimwikiUISelect in ftplugin/vimwiki.vim shadows these inside
+" wiki buffers but dispatches to the same function.
+command! -nargs=0 VimwikiUISelect call nuwiki#commands#wiki_ui_select()
+command! -nargs=0 NuwikiUISelect  call nuwiki#commands#wiki_ui_select()
+
 " Global entry-point mappings — work from any buffer, not just .wiki files.
 " Files are opened directly from config (no LSP required); the server
 " auto-starts via the FileType autocmd once the vimwiki buffer loads.