feat: Add dictionary word lookup feature with cached index

Implements StarDict-based dictionary lookup from the reader menu,
adapted from upstream PR #857 with /.dictionary/ folder path,
std::vector compatibility (PR #802), HTML definition rendering,
orientation-aware button hints, side button hints with CCW text
rotation, sparse index caching to SD card, pronunciation line
filtering, and reorganized reader menu with bookmark stubs.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/util/LookupHistory.h

@@ -0,0 +1,15 @@
+#pragma once
+#include <string>
+#include <vector>
+
+class LookupHistory {
+ public:
+  static std::vector<std::string> load(const std::string& cachePath);
+  static void addWord(const std::string& cachePath, const std::string& word);
+  static void removeWord(const std::string& cachePath, const std::string& word);
+  static bool hasHistory(const std::string& cachePath);
+
+ private:
+  static std::string filePath(const std::string& cachePath);
+  static constexpr int MAX_ENTRIES = 500;
+};