feat(FN-917): add 5 new color themes with full CSS, selector options, and tests

- Add 5 new color theme constants (ocean, forest, sunset, lavender, midnight) to types and index.html
- Add complete CSS theme definitions with color swatches for all 5 themes in styles.css
- Add 5 new theme options to the ThemeSelector component dropdown
- Add comprehensive tests covering all new theme options in ThemeSelector
- No breaking changes; all existing themes remain unchanged

packages/core/src/types.ts

@@ -28,6 +28,11 @@ export const COLOR_THEMES = [
   "dracula",
   "gruvbox",
   "tokyo-night",
+  "catppuccin-mocha",
+  "github-dark",
+  "everforest",
+  "rose-pine",
+  "kanagawa",
 ] as const;
 export type ColorTheme = (typeof COLOR_THEMES)[number];