chore: branded favicon, drop scaffold sprite, wrap long equations

- Replace the generic Vite favicon with a pairing-themed icon (G1/G2
  source nodes converging into the GT target, in the demo's group colours)
- Remove unreferenced public/icons.svg (leftover social-icon scaffold sprite)
- Allow long math-block equations to wrap instead of clip/scroll on phones

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: systemslibrarian

public/favicon.svg

@@ -292,6 +292,8 @@ section.demo-section h2 {
   text-align: center;
   margin: 1rem 0;
   overflow-x: auto;
+  /* let long equations wrap at spaces instead of clipping/scrolling on phones */
+  overflow-wrap: break-word;
 }
 
 .math-block .g1 { color: var(--g1-color); }