Implement search, filtering and favorites for the character list

[gurveers]

Description

Implement search, filtering and favorites for the character list. The Characters page already has UI for search, filters and a favorite button, but the functionality isn't wired up yet.

Done when

• Search text state is added in CharactersPage
• The character list is filtered based on the name entered in the search field
• State for selected filter values is added
• The checkboxes are connected to the filter state
• Characters are filtered by gender, species and status
• Search and multiple filters can be combined
• Favorite state is added, for example based on character id
• isFavorite and onToggleFavorite are passed into CharacterCardSmall
• It's clearly shown whether a character is a favorite or not
• The search field filters characters by name
• The filter checkboxes change which characters are shown
• Search and filters work together
• The favorite button toggles favorite status for the correct character
• Favorite status is shown visually on the card
• Existing layout is preserved