Add custom features section

[Andrew0007-sys]

## What's done
New "Features" section with blocks the merchant can add and reorder.

##Details:

• Section settings: heading, optional subheading (visible_if), column count (range 2–4)
• feature block type: icon, title, description. Limit of 6
• Responsive grid: configured columns on desktop, single column on mobile
• Reveal animation using Dawn's built-in mechanism (scroll-trigger + cascade)
• Card markup extracted into snippets/feature-card.liquid

##Tested:

• Shopify theme check - no errors
• Two sections on the same page don't conflict in styles

[Andrew0007-sys]

opened by mistake, closing