Fixes #15075. Depends on koreader/koreader-base#2287.

Problems with current import (#15040)

1. Notes discarded -- all annotations get hardcoded note = "embedded highlight", overwriting actual /Contents
2. No type filtering -- iterates all annotations including Links, Popups, Widgets
3. Double rendering -- originals stay in PDF while KOReader draws its own on top
4. No deduplication -- running import twice creates duplicates
5. Type not preserved -- all imports become "lighten" regardless of original type

Changes

• pdfdocument.lua: Add getEmbeddedAnnotations() wrapper for the new koreader-base function that returns type, boxes, and contents per markup annotation
• readerhighlight.lua: Replace saveHighlightsFromBoxes() with importEmbeddedAnnotations():
  • Map annotation type to correct drawer (Highlight -> lighten, Underline -> underscore, StrikeOut -> strikeout)
  • Preserve original /Contents as KOReader note
  • Delete imported annotations from PDF (two-phase: delete first, then import)
  • Deduplicate against existing annotations by quadpoint coordinate matching
  • Respect highlight_write_into_pdf naturally (no more disable/restore hack)
• readerbookmark.lua: Rename menu item to "Import embedded annotations", show import/skip counts

This change is