Function validate_encode_dimensions 

pub fn validate_encode_dimensions(
    width: u32,
    height: u32,
) -> Result<(), StegoError>

Validate image dimensions for encoding.

Returns Ok(()) if the dimensions are within acceptable bounds. Called at the start of both ghost_encode and armor_encode.

Errors

• StegoError::ImageTooSmall if either dimension < 200px.
• StegoError::ImageTooLarge if either dimension > 8192px or total pixels > 16M.