Fix: Allow pasting PDF URLs into main table to create entries (JabRef#12911)

* Improve handling of PDF file import behavior

* Add support for handling PDF URLs when pasted

* Revert submodule changes

* Replace Collections.emptyList() with List.of() and improve exception handling

* Change log level from debug to trace for PDF URL

* Registered fix in changelog

* Used getValidFileName for helper method deriveFileNameFromUrl

* Refactor PDF URL detection using FileUtil.isPDFFile

* Move getFileNameFromURL helper method to URLUtil class

Author: Kaan0029

CHANGELOG.md

@@ -117,6 +117,7 @@ Note that this project **does not** adhere to [Semantic Versioning](https://semv
 - We fixed an issue with deleting entries in large libraries that caused it to take a long time. [#8976](https://github.com/JabRef/jabref/issues/8976)
 - We fixed incorrect keyword splitting in `KeywordList.parse` by supporting escaped delimiters (e.g., `\,`, `\\`) [#12810]
 (https://github.com/JabRef/jabref/issues/12810)
+- We fixed an issue where pasting a PDF URL into the main table caused an import error instead of creating a new entry. [#12911](https://github.com/JabRef/jabref/pull/12911)
 - We fixed an issue where libraries would sometimes be hidden when closing tabs with the Welcome tab open. [#12894](https://github.com/JabRef/jabref/issues/12894)
 
 ### Removed