Add KOReader XPath sync support for EPUB navigation

Implements bidirectional conversion between KOReader XPath positions and FreeInkBook character offsets. Uses streaming SAX parsing to match chapter text accounting with ChapterLayout, enabling position sync without requiring DOM or pagination. Handles element ancestry tracking, text offset calculation, and spine index extraction.

test/book_xpath/CMakeLists.txt

@@ -0,0 +1,43 @@
+# BookXPath maps KOReader xpaths <-> FreeInkBook character offsets by
+# streaming chapters through the engine's XmlSax; the suite builds the
+# relevant engine sources host-side. Same FreeInkBook discovery as
+# cpfont_adapter (submodule first, sibling working checkout fallback).
+set(FREEINK_BOOK_DIR "${REPO_ROOT}/freeink-sdk/libs/book/FreeInkBook")
+if(NOT EXISTS "${FREEINK_BOOK_DIR}/include")
+  set(FREEINK_BOOK_DIR "$ENV{HOME}/GitHub/freeink-sdk/libs/book/FreeInkBook")
+endif()
+
+if(NOT EXISTS "${FREEINK_BOOK_DIR}/include")
+  message(WARNING "FreeInkBook sources not found - skipping BookXPathTest")
+else()
+  enable_language(C)  # vendored expat/miniz translation units
+  add_executable(BookXPathTest
+    BookXPathTest.cpp
+    ${REPO_ROOT}/lib/KOReaderSync/BookXPath.cpp
+    ${FREEINK_BOOK_DIR}/src/epub/XmlSax.cpp
+    ${FREEINK_BOOK_DIR}/src/epub/ZipCatalog.cpp
+    ${FREEINK_BOOK_DIR}/src/text/EntityFilter.cpp
+    ${FREEINK_BOOK_DIR}/src/vendor/expat_xmlparse.c
+    ${FREEINK_BOOK_DIR}/src/vendor/expat_xmlrole.c
+    ${FREEINK_BOOK_DIR}/src/vendor/expat_xmltok.c
+    ${FREEINK_BOOK_DIR}/src/vendor/miniz_impl.c
+  )
+
+  target_include_directories(BookXPathTest PRIVATE
+    ${REPO_ROOT}/lib/KOReaderSync
+    ${REPO_ROOT}/lib/Memory
+    ${FREEINK_BOOK_DIR}/include
+    ${FREEINK_BOOK_DIR}/third_party/expat
+    ${FREEINK_BOOK_DIR}/third_party/miniz
+  )
+
+  # The firmware stubs (Logging/Memory) come from a tiny local shim dir.
+  target_include_directories(BookXPathTest BEFORE PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/shim)
+
+  target_link_libraries(BookXPathTest PRIVATE
+    crosspoint_test_common
+    GTest::gtest_main
+  )
+
+  gtest_discover_tests(BookXPathTest)
+endif()