Add FreeInkBook EPUB engine migration guide

Document migration plan from CrossPoint's lib/Epub to FreeInkBook, a memory-efficient clean-room EPUB engine. Covers advantages (O(paragraph+page) memory via SAX parsing, arena allocation, host-testable, full UAX#14 typography, runtime TTF/OTF support), 9-step migration strategy, ESP32-C3 constraints, and integration approach preserving existing UI layer while replacing parsing/layout stack.

lib/EpdFont/EpdFont.cpp

@@ -154,6 +154,21 @@ uint32_t EpdFont::applyLigatures(uint32_t cp, const char*& text) const {
   return cp;
 }
 
+bool EpdFont::hasGlyph(const uint32_t cp) const {
+  const int count = data->intervalCount;
+  if (count > 0) {
+    const EpdUnicodeInterval* intervals = data->intervals;
+    const auto it =
+        std::upper_bound(intervals, intervals + count, cp,
+                         [](uint32_t value, const EpdUnicodeInterval& interval) { return value < interval.first; });
+    if (it != intervals && cp <= (it - 1)->last) return true;
+  }
+  if (data->glyphMissHandler) {
+    return data->glyphMissHandler(data->glyphMissCtx, cp) != nullptr;
+  }
+  return false;
+}
+
 const EpdGlyph* EpdFont::getGlyph(const uint32_t cp) const {
   const int count = data->intervalCount;
   if (count == 0 && !data->glyphMissHandler) return nullptr;