fix(BorderGlow): cancel the intro sweep on cleanup - #1110

BorderGlow's animated intro sweep is started from a useEffect that has no cleanup, and its animateValue helper never keeps the setTimeout / requestAnimationFrame IDs it creates. So once the sweep starts, nothing can stop it:

• Unmounting the card during the ~4s sweep leaves the timers and rAF loops running. They keep writing CSS variables to a detached node (CSS variants) or calling setState on an unmounted component (Tailwind variants).
• Turning animated off doesn't stop the sweep, and the glow stays visible until the sweep finishes.
• Turning it off and on again within those 4 seconds (e.g. the "Animated Intro" switch on the docs page) runs two sweeps at once. Both write --cursor-angle / --edge-proximity on the same frames, and the old sweep's onEnd then hides the glow halfway through the new one.

animateValue now keeps its timer and frame IDs and returns a cancel function. The effect collects the four sweep phases, and its cleanup cancels them and ends the sweep state (sweep-active class / sweepActive state). The change is applied to all four variants and to their public/r/BorderGlow-*.json registry entries.

Reproduction and validation

I bundled the actual component files (before and after) into a small page, ran it in Chrome, and counted the helper's rAF callbacks. All four variants gave the same results:

• ESLint passes for both JS variants. The existing npm run lint failures are in other components and are unchanged.
• A strict TypeScript check passes for both TS variants.
• npm run check:prop-docs passes and git diff --check is clean.
• When the sweep runs normally, its timing, easing and appearance are unchanged.