App/Feature: Arcprompt - Link Previews / Rich Embeds
Issue: YouTube (and potentially other) link previews display placeholder image instead of actual thumbnail.
Description: When a YouTube link is shared or generated in the conversation, the rich preview card displays a generic placeholder image (gray background with mountain icon) rather than the actual video thumbnail/preview image. The link metadata (title, URL, description) loads correctly, but the visual preview image fails to render.
Expected Behavior: The preview card should display the actual YouTube video thumbnail or relevant preview image from the linked content.
Actual Behavior: Only a generic placeholder image is shown in the preview card, making it difficult to visually identify the content before clicking.
