Theme Editor Redesign

Redesigned theme editor with virtual scrolling, mouse support, and Inspect Theme at Cursor.

<div class="showcase-demo"> </div> <!-- Generated by: cargo test --package fresh-editor --test e2e_tests blog_showcase_fresh-0.2.18/theme-editor -- --ignored --> <!-- Then run: scripts/frames-to-gif.sh docs/blog/fresh-0.2.18/theme-editor -->