feat: add RTL support in epub and txt readers (#1700)

Co-authored-by: Zach Nelson <zach@zdnelson.com>

lib/MiniBidi/BidiUtils.h

@@ -0,0 +1,22 @@
+#pragma once
+
+#include <cstdint>
+#include <string>
+#include <vector>
+
+namespace BidiUtils {
+
+// Paragraph-level P2/P3: scan the first N strong chars per word to find base direction.
+inline constexpr int RTL_PARAGRAPH_PROBE_DEPTH = 5;
+
+bool startsWithRtl(const char* utf8, int maxStrongChars = RTL_PARAGRAPH_PROBE_DEPTH);
+
+int detectParagraphLevel(const char* utf8, int fallbackLevel = 0, int maxStrongChars = 64);
+
+// paragraphLevel: -1 = auto-detect, 0 = LTR, 1 = RTL
+bool applyBidiVisual(const char* utf8, std::string& out, int paragraphLevel = -1);
+
+bool computeVisualWordOrder(const std::vector<std::string>& words, bool paragraphIsRtl,
+                            std::vector<uint16_t>& visualOrder);
+
+}  // namespace BidiUtils