Fix vendor mixin issues in Sass - use standard CSS transforms
Replace @include vendor() calls with standard CSS for transform and animation properties. These don't need vendor prefixes in modern browsers and were causing undefined mixin errors.
- _page.scss: Use standard animation/transition
- _hero.scss: Use standard transform
- _scroll-reveal.scss: Use standard transform
Build now compiles successfully without errors (warnings are from HTML5UP legacy libs only).
