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.sh

@@ -70,19 +70,20 @@ 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.
 set nocompatible
-let &runtimepath = '$REPO_ROOT' . ',' . &runtimepath
-let &runtimepath .= ',$VIM_LSP_DIR'
-let &runtimepath .= ',$ASYNC_DIR'
+let &runtimepath = '${REPO_ROOT}' . ',' . &runtimepath
+let &runtimepath .= ',${VIM_LSP_DIR}'
+let &runtimepath .= ',${ASYNC_DIR}'
+let &runtimepath .= ',${DEV_DIR}/calendar-vim'
 
-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_log_level    = 'info'
@@ -113,8 +114,7 @@ augroup NuwikiStart
   autocmd FileType vimwiki call nuwiki#lsp#start()
 augroup END
 
-" Status messages go to :messages so they don't trigger "Press ENTER".
-echomsg '[nuwiki-dev] ready — wiki root: $WIKI_DIR'
+echomsg '[nuwiki-dev] ready — wiki root: ' . g:nuwiki_wiki_root
 echomsg '[nuwiki-dev] :LspStatus for diagnostics, :messages for log'
 EOF
 }
@@ -122,6 +122,7 @@ EOF
 main() {
   ensure_binary
   ensure_vim_lsp
+  ensure_calendar_vim
   seed_wiki
   write_vimrc
   reset_dirs "$VIM_STATE"