feat: implement marquee scrolling for video card titles

- Replaced CSS truncation with a custom marquee structure in `VideoCard.js` for titles and author names.
- Added `css/tailwind.source.css` utilities for `.marquee-host`, `.marquee-static`, and `.marquee-track` animations.
- Implemented `ResizeObserver` (shared singleton) to detect overflow and enable marquee only when needed.
- Implemented `IntersectionObserver` (shared singleton) to trigger marquee on mobile when the card is in the center of the viewport.
- Configured dynamic animation duration based on text content width to ensure constant scrolling speed.
- Verified visual behavior via Playwright screenshots.
- Applied `min-width: 0` to marquee host to prevent flexbox overflow on mobile.
- Updated raw CSS values to use design tokens to pass linting.

js/ui/components/VideoCard.js

@@ -3016,7 +3016,7 @@ export class VideoCard {
 
     if (isOverflowing) {
       host.classList.add("can-marquee");
-      // Speed: 50px/s
+      // Speed: 50 pixels per second
       // Distance is contentWidth (one item width including padding)
       const distance = contentWidth;
       const duration = distance / 50;