feat(koplugin): add support for annotation sync (#3579)

Add bidirectional annotation/highlight sync between KOReader and Readest:

- Add xpointer0/xpointer1 fields to BookNote and DBBookNote types for
  KOReader XPointer positions alongside Readest's CFI format
- Extend transform layer to pass through xpointer fields to/from DB
- Convert CFI→XPointer on push and XPointer→CFI on pull in useNotesSync,
  discarding notes that fail conversion
- Support KOReader's text()[K].N indexed text node format in xcfi.ts for
  paragraphs with inline elements (e.g. <a> page anchors)
- Generate KOReader-compatible XPointers: text().N for single text nodes,
  text()[K].N only when multiple direct text nodes exist
- Skip cfi-inert elements (injected by Readest at runtime) in XPointer
  path building and resolution
- Map highlight colors between KOReader and Readest color systems
- Implement KOReader plugin annotation push/pull with deterministic IDs,
  auto-sync on document open/close, and UIManager refresh on pull
- Refactor koplugin into focused modules: syncauth, syncconfig,
  syncannotations, selfupdate

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker/volumes/db/init/schema.sql

@@ -59,6 +59,8 @@ CREATE TABLE public.book_notes (
   id text NOT NULL,
   type text NULL,
   cfi text NULL,
+  xpointer0 text NULL,
+  xpointer1 text NULL,
   text text NULL,
   style text NULL,
   color text NULL,