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/translations/english.yaml

@@ -285,6 +285,7 @@ STR_HW_RIGHT_LABEL: "Right (4th button)"
 STR_GO_TO_PERCENT: "Go to %"
 STR_GO_HOME_BUTTON: "Go Home"
 STR_SYNC_PROGRESS: "Sync Reading Progress"
+STR_PUSH_AND_SLEEP: "Push Progress & Sleep"
 STR_DELETE_CACHE: "Delete Book Cache"
 STR_CHAPTER_PREFIX: "Chapter: "
 STR_PAGES_SEPARATOR: " pages  |  "