feat(reader): End of Book next-book suggestions (#2499) (#2532)

src/util/NextBookFinder.h

@@ -0,0 +1,15 @@
+#pragma once
+
+#include <string>
+#include <vector>
+
+namespace NextBookFinder {
+
+// Collects up to maxCount book files that order after currentBookPath's filename
+// (natural sort, same ordering as the file browser) within the same folder.
+// Returns bare filenames in sorted order; the current file itself is excluded.
+// Single directory pass keeping only the maxCount best matches, so memory stays
+// bounded regardless of folder size.
+std::vector<std::string> findNextBooks(const std::string& currentBookPath, size_t maxCount);
+
+}  // namespace NextBookFinder