Matugen theme, responsive layout, search icon mask-image fix, and QoL improvements

[mj0x0]

14 commits, demo video below. Happy to split into separate PRs if preferred.

What's in here:

• Fix: search icons render as solid squares. When Vite inlines an SVG as a data URI and the SVG uses single quotes in attributes (e.g. potrace output like google.svg), the unquoted url(${src}) in SearchIcon produces invalid CSS and the mask is silently dropped. Fix: wrap in url("${src}"). Reproduces on main in current Firefox and Chromium.
• Matugen (Material) input template so accent colors follow the system palette.
• Responsive layout using clamp() instead of fixed sizes.
• Scroll / swipe to cycle search engines, with the engine name shown on hover. Mouse-wheel tested; touch implemented but untested on hardware.
• getRandomImage rotates pictures on each load. Added a set of AI-generated images in the Death and Milk style.

recording_small.mp4