Support Multiple Font Colours in Outline

Description: Currently, Outline supports text highlighting with background colours, but does not allow users to change the colour of the text itself. It would be beneficial to add font colour support, similar to editors such as Google Docs, Microsoft Word, or Notion. This would give users additional formatting options for emphasising content, improving readability, and creating more visually structured documentation. Expected Outcome • Users can apply different colors to selected text. • Support for a predefined colour palette, with the possibility of custom colours. • Font colours should coexist with existing text highlighting functionality without conflicts. • Colours should be preserved when content is copied, duplicated, exported, or imported where supported. • Consistent rendering across editing and viewing modes: If a user colors text red while editing a page, the text should still appear red when the page is viewed in read-only mode…