Store link previews in the database

Fixes #301 (closed)

Stores link previews in the database so feeds will load faster and more reliably.

Summary by CodeRabbit

• New Features

  • Introduced dynamic link previews for events and trending links, enhancing how additional content is displayed.

• Refactor

  • Streamlined the link preview retrieval process by eliminating caching and simplifying asynchronous operations for a more efficient experience.

• Chores

  • Updated the database schema to incorporate link preview data, ensuring underlying data consistency with the new display features.