Docs shell polish and fullscreen preview refinements

The docs experience moved closer to the intended browsing flow: lighter navigation, more predictable fullscreen behavior, and better preview framing for canvas-driven demos.

What changed

• Refined the docs sidebar typography, hover treatment, and scroll fade behavior.
• Renamed the component group from WebGL to Canvas to match the current catalog language.
• Added whole-card fullscreen interactions with cleaner controls and reset-to-default props handling.
• Aligned preview framing for OGL-backed components so canvases render at the intended size.

Why it matters

This work tightened the gap between the catalog shell and the demos themselves. Browsing components now feels more like a cohesive docs experience instead of a loose set of demo pages.