fix(kosync): populate chapter field on synced annotations (#4134)

Annotations and bookmarks inserted into KOReader via the Readest sync
plugin were missing the chapter field, which native KOReader highlights
stamp at creation time. Downstream tools that group highlights by
chapter (e.g. obsidian-koreader-highlights, KOReader's own Markdown
exporter) treated these as orphans.

Resolve the chapter title from the xpointer using the same TOC call
that ReaderHighlight uses natively, and include it on both annotation
and bookmark item tables.

Closes #4133

apps/readest.koplugin/syncannotations.lua

@@ -300,6 +300,10 @@ function SyncAnnotations:pull(ui, settings, client, book_hash, meta_hash, dialog
 
                 -- Resolve KOReader page number from xpointer
                 local pageno = ui.document:getPageFromXPointer(xp0) or note.page
+                -- Resolve chapter title so downstream tools can group by chapter,
+                -- matching native KOReader highlight creation behavior.
+                local chapter = ui.toc and ui.toc:getTocTitleByPage(xp0) or nil
+                if chapter == "" then chapter = nil end
 
                 if note_type == "bookmark" then
                     if existing_bookmarks[xp0] then goto continue end
@@ -309,6 +313,7 @@ function SyncAnnotations:pull(ui, settings, client, book_hash, meta_hash, dialog
                         page = xp0,
                         text = note.text or "",
                         note = note.note or "",
+                        chapter = chapter,
                         pageno = pageno,
                         datetime = datetime_str,
                         datetime_updated = datetime_updated_str,
@@ -335,6 +340,7 @@ function SyncAnnotations:pull(ui, settings, client, book_hash, meta_hash, dialog
                         note = note.note or "",
                         drawer = drawer,
                         color = READEST_TO_KO_COLOR[note.color] or "yellow",
+                        chapter = chapter,
                         pageno = pageno,
                         datetime = datetime_str,
                         datetime_updated = datetime_updated_str,