feat: more highlight colours (#3062)

* feat(highlight): extend types and constants for custom hex colours

* feat(highlight): update colour to support hex strings

* refactor(annotator): update component to accept hex colours

* feat(highlight): add colour picker with max 4 custom colors

* feat(settings): add custom colour editor with limit

* refactor: custom highlight colors can only be modified in settings

---------

Co-authored-by: Huang Xin <chrox.huang@gmail.com>

apps/readest-app/src/app/reader/utils/annotatorUtil.ts

@@ -2,9 +2,12 @@ import { HIGHLIGHT_COLOR_HEX } from '@/services/constants';
 import { HighlightColor } from '@/types/book';
 import { SystemSettings } from '@/types/settings';
 
-export const getHighlightColorHex = (settings: SystemSettings, color?: HighlightColor) => {
-  if (!color) return color;
-
+export const getHighlightColorHex = (
+  settings: SystemSettings,
+  color?: HighlightColor,
+): string | undefined => {
+  if (!color) return undefined;
+  if (color.startsWith('#')) return color;
   const customColors = settings.globalReadSettings.customHighlightColors;
   return customColors?.[color] ?? HIGHLIGHT_COLOR_HEX[color];
 };