fix: issue if book href are absolute url and not relative to server (#741)

## Summary

fixing issue if book href are absolute url and not relative to the
server

## Additional Context

* Fixes
https://github.com/crosspoint-reader/crosspoint-reader/issues/632
* https://github.com/harshit181/RSSPub/issues/43

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### AI Usage

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src/util/UrlUtils.cpp

@@ -25,6 +25,10 @@ std::string extractHost(const std::string& url) {
 }
 
 std::string buildUrl(const std::string& serverUrl, const std::string& path) {
+  // If path is already an absolute URL (has protocol), use it directly
+  if (path.find("://") != std::string::npos) {
+    return path;
+  }
   const std::string urlWithProtocol = ensureProtocol(serverUrl);
   if (path.empty()) {
     return urlWithProtocol;