feat: port upstream KOReader sync PRs (#1185, #1217, #1090)

Port three unmerged upstream PRs with adaptations for the fork's
callback-based ActivityWithSubactivity architecture:

- PR #1185: Cache KOReader document hash using mtime fingerprint +
  file size validation to avoid repeated MD5 computation on sync.
- PR #1217: Proper KOReader XPath synchronisation via new
  ChapterXPathIndexer (Expat-based on-demand XHTML parsing) with
  XPath-first mapping and percentage fallback in ProgressMapper.
- PR #1090: Push Progress & Sleep menu option with PUSH_ONLY sync
  mode. Adapted to fork's callback pattern with deferFinish() for
  thread-safe completion. Modified to sleep silently on any failure
  (hash, upload, no credentials) rather than returning to reader.

Made-with: Cursor

lib/I18n/I18nKeys.h

@@ -321,6 +321,7 @@ enum class StrId : uint16_t {
   STR_GO_TO_PERCENT,
   STR_GO_HOME_BUTTON,
   STR_SYNC_PROGRESS,
+  STR_PUSH_AND_SLEEP,
   STR_DELETE_CACHE,
   STR_CHAPTER_PREFIX,
   STR_PAGES_SEPARATOR,