fix(mappings): add global entry-point keymaps and correct <Leader>ww/<Leader>wt targets

Two bugs prevented keymaps from working after a Dein install:

1. <Leader>ww and <Leader>wt both called diary_today() instead of
   wiki_index() / wiki_tab_index(). Fixed in keymaps.lua (Neovim)
   and ftplugin/vimwiki.vim (Vim).

2. All keymaps were buffer-local (<buffer> / buffer=bufnr), so they
   only activated inside an already-open .wiki file. Users had no way
   to reach the wiki from any other buffer, making the plugin appear
   broken on a fresh Vim start.

   Fix: register the eight <Leader>w* entry-point mappings globally —
   in setup() for Neovim (lua/nuwiki/init.lua) and in plugin/nuwiki.vim
   for plain Vim. To avoid a chicken-and-egg LSP dependency, the global
   mappings open files directly from config (wiki_root, diary_rel_path,
   file_extension); the LSP auto-starts via the FileType autocmd once
   the vimwiki buffer loads. Three new autoload helpers
   (open_wiki_path, open_diary_path, open_diary_index_path) provide the
   LSP-free path for the Vim side.

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

autoload/nuwiki/commands.vim

@@ -342,6 +342,36 @@ function! nuwiki#commands#diary_generate_index() abort
   call s:exec('nuwiki.diary.generateIndex', [{ 'uri': s:buf_uri() }])
 endfunction
 
+" ===== Global entry-point helpers (no LSP required) =====
+"
+" These are used by the global mappings in plugin/nuwiki.vim so users can
+" open their wiki from any buffer. Files are opened directly from config;
+" the LSP auto-starts via the FileType autocmd once the buffer loads.
+
+function! nuwiki#commands#open_wiki_path(tab) abort
+  let l:root = expand(get(g:, 'nuwiki_wiki_root', '~/vimwiki'))
+  let l:ext  = get(g:, 'nuwiki_file_extension', '.wiki')
+  if l:ext[0] !=# '.' | let l:ext = '.' . l:ext | endif
+  execute (a:tab ? 'tabedit' : 'edit') . ' ' . fnameescape(l:root . '/index' . l:ext)
+endfunction
+
+function! nuwiki#commands#open_diary_path(day_offset) abort
+  let l:root  = expand(get(g:, 'nuwiki_wiki_root', '~/vimwiki'))
+  let l:ext   = get(g:, 'nuwiki_file_extension', '.wiki')
+  if l:ext[0] !=# '.' | let l:ext = '.' . l:ext | endif
+  let l:diary = get(g:, 'nuwiki_diary_rel_path', 'diary')
+  let l:date  = strftime('%Y-%m-%d', localtime() + a:day_offset * 86400)
+  execute 'edit ' . fnameescape(l:root . '/' . l:diary . '/' . l:date . l:ext)
+endfunction
+
+function! nuwiki#commands#open_diary_index_path() abort
+  let l:root  = expand(get(g:, 'nuwiki_wiki_root', '~/vimwiki'))
+  let l:ext   = get(g:, 'nuwiki_file_extension', '.wiki')
+  if l:ext[0] !=# '.' | let l:ext = '.' . l:ext | endif
+  let l:diary = get(g:, 'nuwiki_diary_rel_path', 'diary')
+  execute 'edit ' . fnameescape(l:root . '/' . l:diary . '/diary' . l:ext)
+endfunction
+
 " ===== List + heading editing =====
 
 function! s:exec_pos(cmd) abort