fix(search): graceful no-match + NuwikiSearch alias (re-audit follow-up)

Re-audit of the just-landed command work found one real bug I introduced
and a convention gap:

- VimwikiSearch / VWS raised a raw E480 on a no-match search; upstream
  reports it gracefully. Both clients now catch it (try/catch in Vim,
  pcall in Neovim) and emit "nuwiki: no match for <pat>".

- Added a NuwikiSearch alias alongside VimwikiSearch/VWS (every other
  command carries a Nuwiki* form).

Gap-doc note corrected: nuwiki's search populates + opens the location
list (shows all matches) where upstream jumps to the first match — logged
as a minor presentation divergence rather than claiming exact parity.

Config + mappings re-audits came back clean (no new gaps, no regressions;
table-mapping rewire verified non-recursive, gLH/gLL/gLR present).

Tests: cmd.VimwikiSearch_no_match_graceful, surface.{Vimwiki,Nuwiki}Search.
Neovim 301, Vim 294/18/21 pass.

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

autoload/nuwiki/commands.vim

@@ -205,7 +205,12 @@ function! nuwiki#commands#search(args) abort
   endif
   let l:ext = l:ext[0] ==# '.' ? l:ext : '.' . l:ext
   let l:glob = l:root ==# '' ? '**' : fnameescape(l:root) . '**/*' . l:ext
-  execute 'lvimgrep /' . escape(l:pat, '/') . '/j ' . l:glob
+  try
+    execute 'lvimgrep /' . escape(l:pat, '/') . '/j ' . l:glob
+  catch /E480/
+    echohl WarningMsg | echom 'nuwiki: no match for ' . l:pat | echohl None
+    return
+  endtry
   lopen
 endfunction