docs: note mirrored page margins as unimplemented

The inner and outer margins are drawn as left and right on every page,
so an even page's text block sits 19mm off where LibreOffice puts it.

CHANGELOG.md

@@ -127,6 +127,7 @@ The gap against Word/LibreOffice, most valuable first. Reviewed 2026-08-08.
 - Alphabetical index and bibliography
 - Line numbering (LibreOffice Tools ▸ Line numbering / Word Layout ▸ Line numbers)
 - Section-level page **size and orientation**: only the margins are per section. A file whose sections disagree on the page size keeps the last one's
+- Mirrored page margins (ODF `style:page-usage="mirrored"`, Word's mirror margins): the inner and outer margins are drawn as left and right on every page, so an even page's text block sits where an odd page's does (measured 19 mm on a two-column scripture extract)
 - Table extras: repeat the header row on every page, keep a row from splitting across pages, sort, sum/formula in a cell, number recognition
 - A list level's own hanging indent: the marker sits at the 0.635 cm both exports write (`LIST_HANGING_CM`), so a wider *left*-set marker overflows where Word moves the text to the next list tab (a **right**-set one — `w:lvlJc`, which is what the built-in Roman numberings use — grows into the margin and is fine). Reading the value back naively also moves the markers of our own ODT exports — LibreOffice draws its own flat hanging at exactly the value odf-kit writes for level 2; see `tests/render-parity/README.md` before building on it
 - Images live as data-URIs in the autosaved JSON, so an image-heavy document can exceed the ~5 MB localStorage quota; `storage/autosave.ts` warns once and a reload restores the last version that still fit. IndexedDB (as `embeddedFontStore.ts` already uses) would lift the ceiling