fix(syntax): colour keywords red/green like the HTML export

All keywords shared one `nuwikiKeyword` group linked to `Todo`, so the editor
showed TODO, DONE and XXX in the same colour. Split into nuwikiKeywordAttn
(TODO/FIXME/XXX, red) and nuwikiKeywordDone (DONE/FIXED/STARTED, green) with
explicit colours so the distinction survives any colorscheme — matching the
export's per-keyword classes.

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

syntax/vimwiki.vim

@@ -89,7 +89,10 @@ syntax match nuwikiCode         /`[^`]\+`/ contains=nuwikiCodeDelim
 syntax match nuwikiCodeDelim    /`/ contained conceal
 
 syntax match nuwikiMathInline   /\$[^$]\+\$/
-syntax match nuwikiKeyword      /\<\(TODO\|DONE\|STARTED\|FIXME\|FIXED\|XXX\)\>/
+" Two keyword groups so the editor can colour them like the HTML export:
+" attention/pending (red) vs resolved/in-progress (green).
+syntax match nuwikiKeywordAttn  /\<\(TODO\|FIXME\|XXX\)\>/
+syntax match nuwikiKeywordDone  /\<\(DONE\|FIXED\|STARTED\)\>/
 
 " Wikilink conceal: hide [[ / ]], and for [[target|desc]] hide target|.
 syntax region nuwikiWikilink start=/\[\[/ end=/\]\]/ keepend contains=nuwikiWikilinkBracket,nuwikiWikilinkTarget
@@ -122,7 +125,11 @@ highlight default nuwikiBold      gui=bold        cterm=bold        term=bold
 highlight default nuwikiItalic    gui=italic      cterm=italic      term=italic
 highlight default link nuwikiCode           String
 highlight default link nuwikiMathInline     Number
-highlight default link nuwikiKeyword        Todo
+" Explicit colours (not a `Todo` link) so the red/green split is visible in any
+" colorscheme. Matches the HTML export: TODO/FIXME/XXX red, DONE/FIXED/STARTED
+" green.
+highlight default nuwikiKeywordAttn gui=bold cterm=bold term=bold guifg=#F44747 ctermfg=203
+highlight default nuwikiKeywordDone gui=bold cterm=bold term=bold guifg=#2EA043 ctermfg=35
 highlight default link nuwikiWikilink       Underlined
 highlight default link nuwikiTransclusion   Identifier
 highlight default link nuwikiUrl            Underlined