fix: Resolve multiple issues with upload to server functionality

[NerdsCorp]

This commit addresses several critical issues with the editor's upload to server feature:

Server-side fixes:

• Changed directory creation from DirectoryInfo.Create() to Directory.CreateDirectory() to ensure parent directories (including the assets folder) are created automatically
• This fixes the issue where the assets folder was never created on the server

Client-side fixes:

• Fixed resource leaks by properly disposing file streams in a finally block
• Improved retry logic to correctly handle and propagate exceptions after all retries fail
• Added FormClosing event handler to save settings when the form is closed
• Implemented persistence of the last selected directory, restoring it on form load
• Added authentication status display to inform users whether they are logged in
• Improved authentication error messages to guide users to log in through the editor
• Fixed issue where server URL and other settings were only saved when clicking Upload

These changes ensure that:

1. The server location is now remembered between sessions
2. The last selected directory is restored, improving user experience
3. The assets folder is automatically created on the server when needed
4. File uploads work reliably with proper error handling and resource management
5. Users receive clear feedback about authentication status

Fixes issues reported in the editor where uploads would silently fail and the assets folder would never be created on the server.