feat(KB-070): add Ayu and One Dark themes to dashboard

- Add Ayu and One Dark to COLOR_THEMES and validThemes arrays
- Add CSS theme variables for both themes in styles.css
- Update ThemeSelector UI to include new theme options
- Extend Theme type to include ayu and one-dark values
- Update tests for ThemeSelector and useTheme hooks
- Add changeset for minor version bump

packages/dashboard/app/hooks/useTheme.ts

@@ -72,6 +72,8 @@ export function useTheme(): UseThemeReturn {
         "monochrome",
         "high-contrast",
         "solarized",
+        "ayu",
+        "one-dark",
       ];
       if (saved && validThemes.includes(saved as ColorTheme)) {
         return saved as ColorTheme;