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>

lua/nuwiki/commands.lua

@@ -566,6 +566,25 @@ function M.list_remove_done_all()
   exec('nuwiki.list.removeDone', uri_args())
 end
 
+-- `:'<,'>VimwikiRemoveDone` — remove done items only within the given line
+-- range (1-indexed, inclusive; converted to the server's 0-indexed range).
+function M.list_remove_done_range(l1, l2)
+  exec('nuwiki.list.removeDone', { { uri = buf_uri(), range = { l1 - 1, l2 - 1 } } })
+end
+
+-- `:[range]VimwikiRemoveDone[!]` dispatcher. `!` → whole buffer; an explicit
+-- range (`range > 0`, e.g. `:'<,'>`) → that line span; otherwise the current
+-- list under the cursor. Mirrors upstream's `-bang -range` form.
+function M.remove_done(bang, range, l1, l2)
+  if bang then
+    M.list_remove_done_all()
+  elseif range and range > 0 then
+    M.list_remove_done_range(l1, l2)
+  else
+    M.list_remove_done()
+  end
+end
+
 -- `:VimwikiRemoveSingleCB` — strip the checkbox from the current item only.
 function M.list_remove_checkbox()
   exec('nuwiki.list.removeCheckbox', pos_args())