- Add sim-analyser-light.svg (#2563eb, light-theme accent); dark
keeps the existing #3b82f6 variant.
- applyTheme() now swaps the favicon href alongside data-theme and
theme-color, so the icon follows toggle click, saved theme on
load, and OS-preference fallback (all route through applyTheme).
- Precache the new asset in the service worker.
