Summary: Tensor.Art adds Avatar function

Why It Matters: Tensor.Art now offers a new way to make videos.

What Changed:

• Add "Sign In" link
• Remove "Spark" section
• Remove "ComfyFlow" section
• Remove "Online Training" section
• Add "Avatar" section
• Update "Create Image" section
• Update "Create Video" section
• Update "AI Tools" section
• Update "Models" section
• Update "Workflows" section
• Add new article about "Avatar & Homepage Update Highlights"
• Update existing articles