fix(parity): close the 2026-06-02 re-audit config/command findings

Implements the remaining fourth-pass findings (gap doc updated):

- list_margin: rework to upstream's buffer-side meaning. Drop the
  nuwiki-only HTML em-margin (renderer field/method + render_page_html
  param removed) and prepend max(0, list_margin) leading spaces to every
  generated bullet in build_toc_text / build_links_text /
  build_tag_links_text / diary::build_index_body; headings stay at col 0.
  From<RawWiki> derives 0 for markdown wikis when unset. Negatives can't
  resolve 'shiftwidth' server-side, so they collapse to zero indent
  (documented divergence).

- diary_months: per-wiki Vec<String> (default 12 English names), threaded
  into the diary-index month labels; missing/empty slots fall back to the
  English name.

- diary_caption_level: widen u8 -> i8 so vimwiki's -1 (min: -1) parses;
  build_index_body clamps < 0 to base tree level 0.

- VimwikiRemoveDone: regain upstream's -range. All four defs are now
  -bang -range, dispatched via remove_done(bang, range, l1, l2) in both
  clients: ! -> whole buffer, explicit range -> new list_remove_done_range
  ({range:[l1-1,l2-1]}), else current list. Server remove_done_edit gained
  an Option<(u32,u32)> range that filters whole-doc victims by start line.

markdown_header_style is deferred: the generators emit vimwiki syntax only
(caption_line never writes markdown headers), so there's no markdown header
to attach the style to. Logged as the "generated-content is vimwiki-only"
intentional divergence pending a later markdown generated-content effort.

Tests: list_margin indent, markdown list_margin-0 default, diary_months
custom + fallback, negative caption_level clamp/parse, ranged remove-done
(server + both keymap harnesses). 553 lsp/core tests pass; clippy clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

autoload/nuwiki/commands.vim

@@ -761,6 +761,26 @@ function! nuwiki#commands#list_remove_done_all() abort
   call s:exec('nuwiki.list.removeDone', l:args)
 endfunction
 
+" `:'<,'>VimwikiRemoveDone` — remove done items only within the given line
+" range (1-indexed, inclusive; converted to the server's 0-indexed range).
+function! nuwiki#commands#list_remove_done_range(l1, l2) abort
+  let l:args = [{ 'uri': s:buf_uri(), 'range': [a:l1 - 1, a:l2 - 1] }]
+  call s:exec('nuwiki.list.removeDone', l:args)
+endfunction
+
+" `:[range]VimwikiRemoveDone[!]` dispatcher. `!` → whole buffer; an explicit
+" range (`a:range > 0`, e.g. `:'<,'>`) → that line span; otherwise the
+" current list under the cursor. Mirrors upstream's `-bang -range` form.
+function! nuwiki#commands#remove_done(bang, range, l1, l2) abort
+  if a:bang
+    call nuwiki#commands#list_remove_done_all()
+  elseif a:range > 0
+    call nuwiki#commands#list_remove_done_range(a:l1, a:l2)
+  else
+    call nuwiki#commands#list_remove_done()
+  endif
+endfunction
+
 " `:VimwikiRemoveSingleCB` — strip the checkbox from the current item only.
 function! nuwiki#commands#list_remove_checkbox() abort
   let l:p = s:cursor_position()