feat(calendar): integrate calendar-vim with wiki diary paths

Wire g:calendar_action/g:calendar_sign to nuwiki diary hooks that
resolve diary paths from the wiki root config instead of calendar-vim's
default ~/diary. Auto-detected on FileType vimwiki when calendar-vim is
present; opt out with g:nuwiki_use_calendar=0 or g:nuwiki_no_calendar.

- autoload/nuwiki/diary.vim: calendar_action/calendar_sign using wiki cfg;
  open diary in the previous window and close the calendar window after.
- autoload/vimwiki/diary.vim: vimwiki# aliases for drop-in compatibility.
- plugin/nuwiki.vim + lua/nuwiki/init.lua: auto-wire hooks, overwriting
  calendar-vim's defaults while respecting user-set custom hooks.
- lua/nuwiki/config.lua: add use_calendar option (on by default).
- development/start-*.sh + _common.sh: clone calendar-vim, fix vimrc var
  expansion, pass wiki root to the Vim/Neovim clients.

development/start-vim-coc.sh

@@ -114,25 +114,27 @@ write_vimrc() {
 
 " Confine state to the dev cache so we never touch the user's real Vim
 " install.
-set viminfo='100,n$VIM_STATE/viminfo
-let &directory = '$VIM_STATE/swap//'
-let &backupdir = '$VIM_STATE/backup//'
-let &undodir = '$VIM_STATE/undo//'
+set viminfo='100,n${VIM_STATE}/viminfo
+let &directory = '${VIM_STATE}/swap//'
+let &backupdir = '${VIM_STATE}/backup//'
+let &undodir = '${VIM_STATE}/undo//'
 
 " Make Vim look for runtime paths in the dev cache. vim-lsp is intentionally
 " absent so nuwiki dispatches jump-to-definition through coc.
 set nocompatible
-let &runtimepath = '$REPO_ROOT' . ',' . &runtimepath
-let &runtimepath .= ',$COC_DIR'
+let &runtimepath = '${REPO_ROOT}' . ',' . &runtimepath
+let &runtimepath .= ',${COC_DIR}'
+let &runtimepath .= ',${DEV_DIR}/calendar-vim'
 
 " Point coc at the generated settings + a private data dir.
-let g:coc_config_home = '$DEV_DIR'
-let g:coc_data_home   = '$COC_DATA'
+let g:coc_config_home = '${DEV_DIR}'
+let g:coc_data_home   = '${COC_DATA}'
 
-let g:nuwiki_binary_path  = '$REPO_ROOT/bin/nuwiki-ls'
-let g:nuwiki_wiki_root    = '$WIKI_DIR'
+let g:nuwiki_binary_path  = '${REPO_ROOT}/bin/nuwiki-ls'
+let g:nuwiki_wiki_root    = '${WIKI_DIR}'
 let g:nuwiki_file_extension = '.wiki'
 let g:nuwiki_syntax       = 'vimwiki'
+let g:nuwiki_diary_rel_path = 'diary'
 let g:nuwiki_log_level    = 'info'
 
 filetype plugin indent on
@@ -153,11 +155,8 @@ augroup NuwikiFtdetect
   autocmd BufRead,BufNewFile *.wiki setfiletype vimwiki
 augroup END
 
-" coc starts the server automatically from coc-settings.json once a vimwiki
-" buffer loads — no explicit nuwiki#lsp#start() needed.
-
-echomsg '[nuwiki-dev] ready (coc.nvim) — wiki root: $WIKI_DIR'
-echomsg '[nuwiki-dev] coc.preferences.jumpCommand = $COC_JUMP'
+echo
+echomsg '[nuwiki-dev] coc.preferences.jumpCommand = ' . '\$COC_JUMP'
 echomsg '[nuwiki-dev] <CR> on a [[link]] should open in the CURRENT window'
 echomsg '[nuwiki-dev] :CocList services for status, :messages for log'
 EOF
@@ -167,6 +166,7 @@ main() {
   ensure_node
   ensure_binary
   ensure_coc
+  ensure_calendar_vim
   write_coc_settings
   seed_wiki
   write_vimrc