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>

lua/nuwiki/health.lua

@@ -0,0 +1,59 @@
+-- lua/nuwiki/health.lua — `:checkhealth nuwiki` target.
+--
+-- Checks per SPEC §7.6: binary exists, is executable, LSP client running,
+-- filetype detection works for `.wiki`.
+
+local M = {}
+
+function M.check()
+  local install = require('nuwiki.install')
+  local config = require('nuwiki.config')
+
+  vim.health.start('nuwiki')
+
+  local bin = install.expected_path()
+  if install.is_installed() then
+    vim.health.ok('binary present at ' .. bin)
+
+    local out = vim.fn.system({ bin, '--version' })
+    if vim.v.shell_error == 0 then
+      vim.health.ok('binary --version: ' .. (out:gsub('\n', ' ')):gsub('^%s+', ''))
+    else
+      vim.health.warn(
+        'binary did not respond to --version',
+        { 'Re-install with :lua require("nuwiki").install()' }
+      )
+    end
+  else
+    vim.health.error(
+      'binary not found at ' .. bin,
+      { 'Run :lua require("nuwiki").install() to install' }
+    )
+  end
+
+  local root = vim.fn.expand(config.options.wiki_root or '')
+  if root ~= '' then
+    if vim.fn.isdirectory(root) == 1 then
+      vim.health.ok('wiki_root exists: ' .. root)
+    else
+      vim.health.warn('wiki_root does not exist: ' .. root)
+    end
+  end
+
+  if vim.fn.exists('#filetypedetect#BufRead#*.wiki') ~= 0
+     or vim.filetype.match({ filename = 'test.wiki' }) == 'vimwiki' then
+    vim.health.ok('filetype detection for *.wiki is wired up')
+  else
+    vim.health.warn('filetype detection for *.wiki not active')
+  end
+
+  local clients = vim.lsp.get_clients and vim.lsp.get_clients({ name = 'nuwiki' })
+    or vim.lsp.get_active_clients({ name = 'nuwiki' })
+  if clients and #clients > 0 then
+    vim.health.ok('LSP client attached (' .. #clients .. ' instance(s))')
+  else
+    vim.health.info('LSP client not yet attached — open a .wiki buffer')
+  end
+end
+
+return M