💄 Update new photos added email template

Revise the email layout and content for new photo notifications, including a preview section and improved messaging. 💄 Update event preserved email template Revise the HTML structure and styling for the event preserved email to enhance readability and user engagement. 💄 Update event tips email content Refine wording for clarity and consistency in event tips emails. 💄 Update review request email content Enhance the clarity and branding of the feedback request email by adding "with Knipsmig" and improving the closing statement for better user engagement. 💄 Update theme colors and styles Revise background and surface colors for various themes to enhance visual appeal and consistency across the application. ✨ Introduce event themes feature Add a variety of color themes for events, enhancing customization options for users. Update views, models, and tests to support this new functionality.