Add AndBible bookmarks import (sqlite -> Xiphos bookmarks.xml)

[LAfricain]

Import bookmarks from AndBible

Adds a way to bring bookmarks created in AndBible
(the Android Bible study app) into Xiphos, via its sqlite backup file.

What this does

• New "Import AndBible Bookmarks" entry next to the existing
  "Import Bookmarks" (BibleTime) menu item.
• Reads AndBible's Room sqlite backup (BibleBookmark, Label,
  BibleBookmarkNotes, BibleBookmarkToLabel tables) and converts it
  into a temporary SwordBookmarks XML file, then merges it into the
  tree using the existing bookmark-parsing code.
• AndBible stores each bookmark as an ordinal position within a
  named SWORD versification system (KJVA, Catholic, Catholic2,
  ...) rather than a plain verse reference. This is decoded back into
  a real verse key using libsword's own VerseKey /
  VersificationMgr, so no separate canon table needs to be
  maintained on the Xiphos side - any versification SWORD already
  knows about is supported automatically.
• AndBible labels become folders (colour included); notes are
  appended to the bookmark description.
• New sqlite3 pkg-config dependency.

Current behaviour: fully-managed folder, not an incremental sync

Every import wipes and rebuilds the whole "Import AndBible" folder
from the current backup, rather than trying to patch it in place.
This gives simple, duplicate-free, predictable behaviour - additions,
edits and label changes made in AndBible all show up correctly just
by reimporting - but at the cost of not preserving anything filed by
hand into that folder, and of no distinction between "what changed"
and "what didn't". The user is warned about this both before
(confirmation dialog if a previous import exists) and after
(summary dialog) each import.

This is a first step, not the end state

A few things are deliberately left out of this first version, to keep
it reviewable:

• Incremental import. Rather than replace-the-whole-folder, a
  future version could diff the existing imported bookmarks against
  the new backup (by matching verse key + module + folder) and only
  add/update/remove what actually changed, instead of rebuilding
  everything on every import.
• Retrieving AndBible's own cloud sync directly. AndBible has a
  native cloud sync feature (Nextcloud/Google Drive) that goes beyond
  the simple backup file this PR reads. Being able to pull bookmarks
  straight from that sync store - rather than requiring the user to
  manually export/copy a sqlite backup file - would turn this from a
  one-off import into something closer to a real sync. That's a
  separate, bigger piece of work (different, and only partly
  understood, on-disk/remote format) and out of scope here.