fix: use white text for selected dropdown items in dark mode

Selected dropdown items now use maximum contrast in dark mode:
- Primary text: white (was brand.200)
- Secondary text: gray.200 (was brand.300)

This ensures selected items stand out clearly against the gray.700
background with optimal readability.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

apps/web/src/app/create/worksheets/addition/components/OrientationPanel.tsx

@@ -398,7 +398,7 @@ export function OrientationPanel({
                                 fontWeight: 'semibold',
                                 color: isSelected
                                   ? isDark
-                                    ? 'brand.200'
+                                    ? 'white'
                                     : 'brand.700'
                                   : isDark
                                     ? 'gray.200'
@@ -412,7 +412,7 @@ export function OrientationPanel({
                                 fontSize: 'xs',
                                 color: isSelected
                                   ? isDark
-                                    ? 'brand.300'
+                                    ? 'gray.200'
                                     : 'brand.600'
                                   : isDark
                                     ? 'gray.400'