feat: implement CSS enumeration through OPF directory when missing from manifest (#2148)

lib/FsHelpers/FsHelpers.cpp

@@ -129,6 +129,8 @@ bool hasTxtExtension(std::string_view fileName) { return checkFileExtension(file
 
 bool hasMarkdownExtension(std::string_view fileName) { return checkFileExtension(fileName, ".md"); }
 
+bool hasCssExtension(std::string_view fileName) { return checkFileExtension(fileName, ".css"); }
+
 std::string extractFolderPath(const std::string& filePath) {
   const auto lastSlash = filePath.find_last_of('/');
   if (lastSlash == std::string::npos || lastSlash == 0) {

lib/FsHelpers/FsHelpers.h

@@ -58,6 +58,11 @@ inline bool hasTxtExtension(const String& fileName) {
 // Check for .md extension (case-insensitive)
 bool hasMarkdownExtension(std::string_view fileName);
 
+// Check for .css extension (case-insensitive)
+bool hasCssExtension(std::string_view fileName);
+inline bool hasCssExtension(const String& fileName) {
+  return hasCssExtension(std::string_view{fileName.c_str(), fileName.length()});
+}
 std::string extractFolderPath(const std::string& filePath);
 
 /**