fix: enable recursive search, fix openssl download URL and resolve windows path quoting errors

[l1n00]

This PR resolves critical bugs and adds a new feature:

1. Recursive Subfolder Search: Replaced os.listdir with Path.rglob to recursively discover all .p7m files inside the selected directory and its subfolders.
2. Fixed Broken OpenSSL Download URL (404 Error): The previous hardcoded URL for the OpenSSL installer (v3.3.2) was returning a 404 error. Updated the installer to download Win64OpenSSL_Light-3_5_7.exe (a stable, lightweight version).
3. Resolved "Path Not Found" Errors on Windows: Invocations of subprocess.run with shell=True and double-quoted command strings caused parsing errors on Windows when spaces were present in file/directory paths. By moving to a structured list of arguments (with shell=False), these quoting issues are completely resolved.
4. Robust UAC Elevation Handler: Added a ctypes-based Windows UAC elevation handler to run the installer, prompting the user for permissions if running without administrative rights.