test(config): verify Vim/Neovim config payload parity

Expose the init_options payload builders publicly in both clients
(M.init_options/M.server_settings in Lua, nuwiki#lsp#settings() in Vim) so
they can be inspected. Add editor harnesses that dump each client's
server-bound config as deterministic key=value lines and diff against a
shared golden file: nvim == golden and vim == golden together prove the two
clients send identical config. Add a server-side test asserting the Vim flat
shape and the Neovim {nuwiki:{...}} wrapper desugar to the same WikiConfig.
Wire both harnesses into CI.

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

development/tests/test-config-vim.vim

@@ -0,0 +1,50 @@
+" development/tests/test-config-vim.vim — Vim counterpart of
+" test-config.lua. Dumps the Vim client's `initialization_options` payload
+" (nuwiki#lsp#settings()) for the same two scenarios as the Neovim harness,
+" as byte-identical `key=value` lines, so both can be diffed against the
+" shared golden development/tests/config-expected.txt.
+"
+" "nvim == golden" and "vim == golden" together prove Vim/Neovim config
+" parity for everything the server consumes.
+
+let s:out = $NUWIKI_CONFIG_OUT
+let s:lines = []
+
+function! s:dump(payload) abort
+  call add(s:lines, 'wiki_root=' . a:payload.wiki_root)
+  call add(s:lines, 'file_extension=' . a:payload.file_extension)
+  call add(s:lines, 'syntax=' . a:payload.syntax)
+  call add(s:lines, 'log_level=' . a:payload.log_level)
+  if has_key(a:payload, 'wikis')
+    let l:i = 0
+    for l:w in a:payload.wikis
+      for l:k in sort(keys(l:w))
+        call add(s:lines, printf('wikis[%d].%s=%s', l:i, l:k, l:w[l:k]))
+      endfor
+      let l:i += 1
+    endfor
+  endif
+endfunction
+
+" Scenario 1: defaults (no globals set).
+unlet! g:nuwiki_wiki_root g:nuwiki_file_extension g:nuwiki_syntax
+unlet! g:nuwiki_log_level g:nuwiki_wikis
+call add(s:lines, '[default]')
+call s:dump(nuwiki#lsp#settings())
+
+" Scenario 2: same representative config as the Neovim harness.
+let g:nuwiki_wiki_root      = '/tmp/base'
+let g:nuwiki_file_extension = '.md'
+let g:nuwiki_syntax         = 'vimwiki'
+let g:nuwiki_log_level      = 'debug'
+let g:nuwiki_wikis = [
+      \ { 'name': 'personal', 'root': '/tmp/personal',
+      \   'file_extension': '.wiki', 'index': 'home',
+      \   'diary_rel_path': 'journal' },
+      \ { 'name': 'work', 'root': '/tmp/work' },
+      \ ]
+call add(s:lines, '[sample]')
+call s:dump(nuwiki#lsp#settings())
+
+call writefile(s:lines, s:out)
+qall!