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.sh

@@ -0,0 +1,58 @@
+#!/usr/bin/env bash
+#
+# development/tests/test-config-vim.sh — Vim counterpart of test-config.sh.
+#
+# Runs development/tests/test-config-vim.vim under headless Vim, which dumps
+# the Vim client's `initialization_options` payload (nuwiki#lsp#settings())
+# as `key=value` lines, then diffs against the shared golden
+# config-expected.txt. Matching the same golden the Neovim harness uses is
+# what proves Vim/Neovim config parity.
+#
+# Exit code: 0 when the payload matches the golden, 1 otherwise. Skips
+# (exit 0) when vim is not installed.
+
+set -euo pipefail
+
+REPO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
+
+log() { printf '\033[1;34m[config-vim]\033[0m %s\n' "$*"; }
+
+if ! command -v vim >/dev/null 2>&1; then
+  log 'vim not installed — skipping'
+  exit 0
+fi
+
+TMP="$(mktemp -d -t nuwiki-config-vim-test-XXXXXX)"
+trap 'rm -rf "$TMP"' EXIT
+
+GOLDEN="$REPO_ROOT/development/tests/config-expected.txt"
+OUT="$TMP/vim-config.txt"
+
+VIMRC="$TMP/vimrc"
+cat > "$VIMRC" <<EOF
+set nocompatible
+let &runtimepath = '$REPO_ROOT' . ',' . &runtimepath
+filetype plugin indent on
+EOF
+
+log 'running Vim config harness…'
+# `</dev/null` so ex-mode doesn't hang on stdin; `timeout` guards CI.
+NUWIKI_CONFIG_OUT="$OUT" \
+  timeout 30 vim -e -s -u "$VIMRC" \
+    -c "source $REPO_ROOT/development/tests/test-config-vim.vim" \
+    </dev/null >"$TMP/vim.log" 2>&1 || true
+
+if [[ ! -f "$OUT" ]]; then
+  echo 'config harness produced no output' >&2
+  echo '--- vim log ---' >&2
+  cat "$TMP/vim.log" >&2 || true
+  exit 1
+fi
+
+if diff -u "$GOLDEN" "$OUT"; then
+  log 'Vim config payload matches golden ✓'
+  exit 0
+fi
+
+echo 'Vim config payload DIVERGED from golden (see diff above)' >&2
+exit 1