feat(vim): conceal markup delimiters when conceallevel=2

Set conceallevel=2 and concealcursor=nc on .wiki buffers and add
contained `conceal` matches for the bold/italic/code delimiters and
wikilink brackets/targets. The static-fallback rendering now mirrors
what the Neovim semantic-token path produced: *bold* shows as bold
without the asterisks, [[target|desc]] shows just "desc", etc.

The wikilink region uses an inline `contains=` (no line continuation)
because some Vim builds (notably Homebrew Vim 9.2) raise E10 on the
leading `\\ contains=...` form even though the surrounding region
parses fine.

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

ftplugin/vimwiki.vim

@@ -18,8 +18,10 @@ setlocal comments=:%%
 setlocal formatoptions+=ron
 setlocal suffixesadd=.wiki
 setlocal iskeyword+=-
+setlocal conceallevel=2
+setlocal concealcursor=nc
 
-let b:undo_ftplugin = 'setlocal commentstring< comments< formatoptions< suffixesadd< iskeyword<'
+let b:undo_ftplugin = 'setlocal commentstring< comments< formatoptions< suffixesadd< iskeyword< conceallevel< concealcursor<'
 
 if !has('nvim')
   " ===== Plain Vim path =====

syntax/vimwiki.vim

@@ -68,12 +68,24 @@ syntax region nuwikiPreformatted start=/^{{{/ end=/^}}}/ keepend
 syntax region nuwikiMathBlock    start=/^{{\$/ end=/^}}\$/ keepend
 syntax match nuwikiPlaceholder  /^%\(title\|nohtml\|template\|date\)\>.*$/
 
-syntax match nuwikiBold         /\*[^*]\+\*/
-syntax match nuwikiItalic       /\<_[^_]\+_\>/
-syntax match nuwikiCode         /`[^`]\+`/
+syntax match nuwikiBold         /\*[^*]\+\*/ contains=nuwikiBoldDelim
+syntax match nuwikiBoldDelim    /\*/ contained conceal
+
+syntax match nuwikiItalic       /\<_[^_]\+_\>/ contains=nuwikiItalicDelim
+syntax match nuwikiItalicDelim  /_/ contained conceal
+
+syntax match nuwikiCode         /`[^`]\+`/ contains=nuwikiCodeDelim
+syntax match nuwikiCodeDelim    /`/ contained conceal
+
 syntax match nuwikiMathInline   /\$[^$]\+\$/
 syntax match nuwikiKeyword      /\<\(TODO\|DONE\|STARTED\|FIXME\|FIXED\|XXX\)\>/
-syntax region nuwikiWikilink    start=/\[\[/ end=/\]\]/ keepend
+
+" Wikilink conceal: hide [[ / ]], and for [[target|desc]] hide target|.
+syntax region nuwikiWikilink start=/\[\[/ end=/\]\]/ keepend contains=nuwikiWikilinkBracket,nuwikiWikilinkTarget
+syntax match nuwikiWikilinkBracket /\[\[/ contained conceal
+syntax match nuwikiWikilinkBracket /\]\]/ contained conceal
+syntax match nuwikiWikilinkTarget  /[^|\]]*|/ contained conceal
+
 syntax region nuwikiTransclusion start=/{{[^{]/ end=/}}/ keepend
 syntax match nuwikiUrl          /\<\(https\?\|ftp\|mailto\|file\):\/\?\/\?\S\+/