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>

autoload/nuwiki/lsp.vim

@@ -91,3 +91,11 @@ function! s:settings() abort
   endif
   return l:cfg
 endfunction
+
+" Public accessor for the `initialization_options` payload. Mirrors the
+" Neovim client's `require('nuwiki.lsp').init_options()` so the config
+" parity harness can inspect the exact dict each client sends to the
+" server.
+function! nuwiki#lsp#settings() abort
+  return s:settings()
+endfunction