phase 9: editor glue — plugin, LSP wiring, install, health, docs

P5 + P6 resolved (SPEC §11): Neovim 0.11+ and Vim 9.1+.

Universal Vim entry:
- plugin/nuwiki.vim dispatches Vim vs Neovim. Neovim path waits for
  the user's `require('nuwiki').setup()` call; Vim path starts the
  LSP client on `FileType vimwiki` and exposes `:NuwikiInstall`.
- ftdetect/nuwiki.vim associates `*.wiki` with the `vimwiki` filetype.
- ftplugin/nuwiki.vim sets commentstring + comments + formatoptions +
  suffixesadd + iskeyword, with a clean `b:undo_ftplugin`.
- syntax/nuwiki.vim ships default `@vimwiki*` highlight links for the
  semantic-token legend (with `level1..6` + `centered` modifiers),
  plus a minimal regex fallback so static highlighting works before
  the LSP attaches.

Lua glue (Neovim 0.11+):
- init.lua exposes setup() / install() / health() — wiring only per
  SPEC §6.2.
- config.lua holds the §7.5 schema (wiki_root / file_extension /
  syntax / log_level) and a tbl_deep_extend apply().
- lsp.lua registers via `vim.lsp.config{} + vim.lsp.enable` on 0.11+;
  falls back to a FileType autocmd calling `vim.lsp.start` on older
  builds. Root dir walks up for `.git` / `.nuwiki`, then uses
  wiki_root.
- install.lua does target-triple detection (Linux gnu/musl x x86_64/
  aarch64, macOS arm/x86, Windows), curl+tar download from the
  release URL, cp/chmod into bin/, with a cargo fallback. Honours
  `g:nuwiki_build_from_source`.
- health.lua implements `:checkhealth nuwiki` per §7.6.

VimL glue (Vim 9.1+):
- autoload/nuwiki/lsp.vim follows §7.4 preference order:
  vim-lsp (calls `lsp#register_server`) → coc.nvim (prints the
  coc-settings.json snippet) → error.
- scripts/download_bin.vim mirrors the Lua installer for Dein /
  vim-plug build hooks — same target triples, same download →
  fallback → cargo build chain.

Help: doc/nuwiki.txt with tags for install (lazy.nvim / vim-plug /
Dein), config options, health, LSP feature list, `:NuwikiInstall`.

Rust workspace unchanged this phase; 172 tests still green locally.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

syntax/nuwiki.vim

@@ -1,2 +1,89 @@
-" syntax/nuwiki.vim — static fallback syntax highlighting (no LSP required).
-" Implementation deferred to Phase 9 (Editor Glue).
+" syntax/nuwiki.vim — default highlight groups for nuwiki.
+"
+" Two responsibilities:
+"   1. Default `@vimwiki*` highlight groups for the LSP semantic tokens
+"      (SPEC §11 P7). Loaded eagerly so the very first hover/highlight
+"      cycle after server startup already has colours.
+"   2. A small regex-based fallback so static highlighting works on
+"      buffers where the LSP isn't running yet.
+
+if exists('b:current_syntax')
+  finish
+endif
+
+" ===== Semantic-token defaults (Neovim's TS-style @group names) =====
+
+" Headings — level modifiers map to progressively softer accents.
+highlight default link @vimwikiHeading              Title
+highlight default link @vimwikiHeading.level1       Title
+highlight default link @vimwikiHeading.level2       Function
+highlight default link @vimwikiHeading.level3       Identifier
+highlight default link @vimwikiHeading.level4       Type
+highlight default link @vimwikiHeading.level5       Constant
+highlight default link @vimwikiHeading.level6       PreProc
+highlight default link @vimwikiHeading.centered     Title
+
+" Inline text styling.
+highlight default link @vimwikiBold                 markdownBold
+highlight default link @vimwikiItalic               markdownItalic
+highlight default link @vimwikiBoldItalic           markdownBoldItalic
+highlight default link @vimwikiStrikethrough        Comment
+highlight default link @vimwikiSuperscript          Number
+highlight default link @vimwikiSubscript            Number
+
+" Code + math.
+highlight default link @vimwikiCode                 String
+highlight default link @vimwikiCodeBlock            String
+highlight default link @vimwikiMath                 Number
+highlight default link @vimwikiMathBlock            Number
+
+" Links + transclusions.
+highlight default link @vimwikiWikilink             Underlined
+highlight default link @vimwikiExternalLink         Underlined
+highlight default link @vimwikiUrl                  Underlined
+highlight default link @vimwikiTransclusion         Identifier
+
+" Misc.
+highlight default link @vimwikiKeyword              Todo
+highlight default link @vimwikiColor                Constant
+highlight default link @vimwikiComment              Comment
+highlight default link @vimwikiDefinitionTerm       Statement
+
+" ===== Static fallback (no LSP required) =====
+
+syntax case match
+
+syntax match nuwikiHeading      /^\s*=\{1,6}\s.\{-}\s=\{1,6}\s*$/
+syntax match nuwikiHorizontal   /^-\{4,}\s*$/
+syntax match nuwikiCommentLine  /^%%.*$/
+syntax region nuwikiCommentBlock start=/^%%+/ end=/+%%/ keepend
+syntax region nuwikiPreformatted start=/^{{{/ end=/^}}}/ keepend
+syntax region nuwikiMathBlock    start=/^{{\$/ end=/^}}\$/ keepend
+syntax match nuwikiPlaceholder  /^%\(title\|nohtml\|template\|date\)\>.*$/
+
+syntax match nuwikiBold         /\*[^*]\+\*/
+syntax match nuwikiItalic       /\<_[^_]\+_\>/
+syntax match nuwikiCode         /`[^`]\+`/
+syntax match nuwikiMathInline   /\$[^$]\+\$/
+syntax match nuwikiKeyword      /\<\(TODO\|DONE\|STARTED\|FIXME\|FIXED\|XXX\)\>/
+syntax region nuwikiWikilink    start=/\[\[/ end=/\]\]/ keepend
+syntax region nuwikiTransclusion start=/{{[^{]/ end=/}}/ keepend
+syntax match nuwikiUrl          /\<\(https\?\|ftp\|mailto\|file\):\/\?\/\?\S\+/
+
+highlight default link nuwikiHeading        Title
+highlight default link nuwikiHorizontal     Comment
+highlight default link nuwikiCommentLine    Comment
+highlight default link nuwikiCommentBlock   Comment
+highlight default link nuwikiPreformatted   String
+highlight default link nuwikiMathBlock      Number
+highlight default link nuwikiPlaceholder    PreProc
+highlight default link nuwikiBold           Bold
+highlight default link nuwikiItalic         Italic
+highlight default link nuwikiCode           String
+highlight default link nuwikiMathInline     Number
+highlight default link nuwikiKeyword        Todo
+highlight default link nuwikiWikilink       Underlined
+highlight default link nuwikiTransclusion   Identifier
+highlight default link nuwikiUrl            Underlined
+
+let b:current_syntax = 'vimwiki'