test(calendar): add Vim + Neovim integration harnesses

Add headless harnesses covering the calendar-vim integration, wired into
CI alongside the existing keymap/config suites:

- test-calendar-vim.sh/.vim (+ -optout.vim): pure-VimL diary hooks
  (calendar_sign markers, calendar_action path resolution from wiki root,
  calendar window close), plugin/nuwiki.vim hook auto-wiring that
  overrides calendar-vim's defaults, and opt-out via g:nuwiki_use_calendar
  and g:nuwiki_no_calendar. Uses a stub calendar-vim on the runtimepath.
- test-calendar.sh/.lua: Neovim setup() wiring + window-close under the
  real window API, and opt-out via use_calendar = false.

Fixes surfaced by the suite:
- diary.vim: new diary entries set filetype 'vimwiki' (was the raw
  extension, e.g. 'wiki'); the stray FileType autocmd also blocked the
  calendar window from closing.
- init.lua: drop the redundant Neovim FileType autocmd (plugin/nuwiki.vim
  already wires both editors) and translate use_calendar=false into
  g:nuwiki_no_calendar so the opt-out actually disables wiring.

development/tests/test-calendar.sh

@@ -0,0 +1,106 @@
+#!/usr/bin/env bash
+#
+# development/tests/test-calendar.sh — calendar-vim integration harness (Neovim).
+#
+# Drives development/tests/test-calendar.lua under headless Neovim to cover the
+# pieces specific to the Lua entry point:
+#   * require('nuwiki').setup() wiring g:calendar_action / g:calendar_sign and
+#     overriding calendar-vim's own defaults,
+#   * calendar_action's window-close behaviour under the real window API,
+#   * opting out with use_calendar = false.
+#
+# A stub calendar-vim on the runtimepath provides :Calendar and seeds the
+# default hook names. The LSP binary is built (setup() registers the client);
+# the calendar paths themselves don't need the server.
+#
+# Exit: 0 when both runs are green, 1 otherwise. Skips (0) without nvim.
+
+set -euo pipefail
+
+REPO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
+TMP="$(mktemp -d -t nuwiki-calendar-test-XXXXXX)"
+trap 'rm -rf "$TMP"' EXIT
+
+log() { printf '\033[1;34m[calendar]\033[0m %s\n' "$*"; }
+
+if ! command -v nvim >/dev/null 2>&1; then
+  log 'nvim not installed — skipping'
+  exit 0
+fi
+
+# setup() registers the LSP client, so build the binary like the other
+# Neovim harnesses do (incremental, fast).
+BIN="$REPO_ROOT/bin/nuwiki-ls"
+log 'building nuwiki-ls (release, incremental)…'
+cargo build --release -p nuwiki-ls --manifest-path "$REPO_ROOT/Cargo.toml" >/dev/null
+mkdir -p "$REPO_ROOT/bin"
+ln -sf "$REPO_ROOT/target/release/nuwiki-ls" "$BIN"
+
+# --- Scratch wiki with one seeded diary entry (2026-05-30) ----------------
+WIKI="$TMP/wiki"
+mkdir -p "$WIKI/diary"
+echo "= index =" > "$WIKI/index.wiki"
+echo "= 2026-05-30 =" > "$WIKI/diary/2026-05-30.wiki"
+
+# --- Stub calendar-vim ----------------------------------------------------
+CAL="$TMP/calendar-vim"
+mkdir -p "$CAL/plugin" "$CAL/autoload"
+cat > "$CAL/plugin/calendar.vim" <<'EOF'
+if exists('g:loaded_calendar_stub') | finish | endif
+let g:loaded_calendar_stub = 1
+let g:calendar_action = get(g:, 'calendar_action', 'calendar#diary')
+let g:calendar_sign   = get(g:, 'calendar_sign', 'calendar#sign')
+command! -nargs=* Calendar echo 'stub calendar'
+EOF
+cat > "$CAL/autoload/calendar.vim" <<'EOF'
+function! calendar#open(...) abort
+endfunction
+function! calendar#diary(...) abort
+endfunction
+function! calendar#sign(...) abort
+  return 0
+endfunction
+EOF
+
+write_init() {
+  local file="$1" use_calendar="$2"
+  cat > "$file" <<EOF
+vim.opt.runtimepath:prepend('$REPO_ROOT')
+vim.opt.runtimepath:append('$CAL')
+vim.g.nuwiki_binary_path = '$BIN'
+vim.g.nuwiki_wiki_root = '$WIKI'
+vim.g.nuwiki_file_extension = '.wiki'
+vim.g.nuwiki_diary_rel_path = 'diary'
+require('nuwiki').setup({ wiki_root = '$WIKI', use_calendar = $use_calendar })
+EOF
+}
+
+run() {
+  local label="$1" init="$2" mode="$3"
+  local results="$TMP/results-$label.txt"
+  log "running $label harness…"
+  NUWIKI_CALENDAR_RESULTS="$results" \
+  NUWIKI_CALENDAR_WIKI="$WIKI" \
+  NUWIKI_CALENDAR_MODE="$mode" \
+    timeout 60 nvim --clean -u "$init" --headless \
+      -c "luafile $REPO_ROOT/development/tests/test-calendar.lua" \
+      >"$TMP/$label.log" 2>&1 || true
+  if [[ ! -f "$results" ]]; then
+    echo "calendar $label harness produced no output" >&2
+    echo "--- nvim log ---" >&2
+    cat "$TMP/$label.log" >&2 || true
+    return 1
+  fi
+  cat "$results"
+  grep -qE '^SUMMARY: [0-9]+ passed, 0 failed' "$results"
+}
+
+INIT_ON="$TMP/init-on.lua"
+INIT_OFF="$TMP/init-off.lua"
+write_init "$INIT_ON" 'true'
+write_init "$INIT_OFF" 'false'
+
+rc=0
+run 'default' "$INIT_ON" 'default' || rc=1
+run 'optout' "$INIT_OFF" 'optout' || rc=1
+exit $rc