chore(release): 0.5.0 — first plugin-only release

First tagged release after extracting the Rust server to nuwiki-rs. The
plugin and nuwiki-ls now version independently; 0.5.0 marks the split.
Bumps g:nuwiki_version (surfaced by :NuwikiShowVersion).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

plugin/nuwiki.vim

@@ -15,7 +15,7 @@ let g:loaded_nuwiki = 1
 " Plugin version, surfaced by :VimwikiShowVersion / :NuwikiShowVersion.
 " Set before the Neovim early-return below so both clients see the global.
 if !exists('g:nuwiki_version')
-  let g:nuwiki_version = '0.4.2'
+  let g:nuwiki_version = '0.5.0'
 endif
 
 " Resolve the plugin root NOW, while this script is being sourced and