shop: rename laptop handle to ac-blank-laptop
Product was retitled "AC Blank Laptop" in Shopify and the handle moved
from laptops_ac-native-laptop_26-4-17-12-51 to
laptops_ac-blank-laptop_26-4-17-12-51. Shopify auto-301-redirects the
old URL, but update the two hardcoded references so visitors skip the
redirect hop:
- blank.mjs SHOP_URL + header comment
- lacma-2026/index.html: 2 product links in the demo-hardware card
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>