fix: black SVG icons now render white — invert(1) filter; proper fullscreen icon

- Pipedal SVGs have no fill (default black) — added invert(0.95) brightness(2)
  to render them white on dark backgrounds
- Status bar icons: brightness(0.7) was making them invisible on dark bg
- Fullscreen icon: replaced ic_drawer_2 (cabinet) with proper inline
  Material-style expand SVG in amber

src/BlockChain.jsx

@@ -95,7 +95,7 @@ function BlockIcon({ type, size = 14, style = {} }) {
       alt={type || 'fx'}
       style={{
         width: size, height: size, flexShrink: 0,
-        filter: 'brightness(1.2) contrast(1.1)',
+        filter: 'invert(0.95) brightness(2)',
         objectFit: 'contain',
         ...style,
       }}