fix(app): improve light mode theming

- Make PaseoLogo theme-aware (uses foreground color instead of hardcoded white)
- Add shadow tokens (sm/md/lg) to theme with per-scheme opacity, radius, and offset
- Replace all 16 hardcoded shadow instances with spreadable theme.shadow tokens
- Fix button icon color for default variant (use accentForeground, not foreground)
- Fix dark background flash on startup (root layout used hardcoded darkTheme)
- Add theme.colorScheme to replace fragile hex-string dark mode detection
- Add scrollbarHandle and surfaceWorkspace tokens to eliminate isDark branching

packages/app/src/components/git-diff-pane.tsx

@@ -86,9 +86,8 @@ interface HighlightedTextProps {
 
 function HighlightedText({ tokens, lineType }: HighlightedTextProps) {
   const { theme } = useUnistyles();
-  const isDark = theme.colors.surface0 === "#181B1A";
+  const isDark = theme.colorScheme === "dark";
 
-  // Get color for a highlight style
   const getTokenColor = (style: HighlightStyle | null): string => {
     const baseColor = isDark ? "#c9d1d9" : "#24292f";
     if (!style) return baseColor;