I've added the shareCard function that uses the exact same canvas drawing logic as the downloadCard function. When the "Share & Get Rewards!" button is clicked, it generates the greeting card image using identical rendering and then attempts to share it using the Web Share API, falling back to download if sharing isn't supported. This ensures both buttons produce the same high-quality greeting card image output.

I've updated the share function to first download the greeting card image and then automatically initiate Facebook sharing. The process now downloads the card, waits 1 second, then attempts to share via the Web Share API (on mobile) or opens a Facebook share dialog (on desktop) with the card's message content. This ensures users get both the downloaded image and automatic Facebook sharing functionality.