feat(homepage): create landing page with slideshow and upcoming events

[McPringle]

User Story

As a visitor,
I want to see an attractive homepage with photos of past events and information about upcoming events,
so that I get an impression of the community’s activities and can quickly discover upcoming opportunities to participate.

---

Important Note

For implementing the slideshow, the FlowingCode Carousel Add-on for Vaadin could be considered as a potential component.

---

Acceptance Criteria

• Slideshow

  • The homepage displays a slideshow with a selection of photos from past events.
  • The slideshow automatically cycles through the photos.
  • Users can manually navigate between photos.

• Upcoming Events Preview

  • Below the slideshow, the next three upcoming events are displayed.
  • Events are shown in chronological order (soonest first).
  • Each event is displayed as a card, consistent with the design of the "Events" overview page.

• More Events Card

  • Instead of a simple text link, a dedicated card is displayed after the three events.
  • The card clearly indicates the option to view more events.
  • Clicking the card redirects the user to the main Events page, where all events are listed.

• Testing

  • Manual testing is performed successfully on both desktop and mobile devices.
  • Full automated test coverage is implemented for the added code.
  • All automated tests pass.

[danncortes]

I can start this one