Redesign garden page with curated sections and sort/filter

Created by: jedmund

Summary

• Redesign /garden index from flat category lists to curated sections: currently enjoying, bangers, recently added, and category browse links
• Add sort/filter controls to /garden/[category] pages (A-Z, recently added, recently released, bangers only)
• Extract GardenCard component to share card markup between index and category pages
• Add GardenSortFilter component with sort dropdown and bangers toggle
• Add sort and bangers query params to the category API endpoint

Test plan

• /garden shows curated sections (currently enjoying, bangers, recently added, browse)
• Sections only appear when they have items
• Category cards link to /garden/[category] and show item counts
• Sort dropdown on category pages changes URL params and re-sorts
• "Bangers only" toggle filters to favorites
• Combining sort + filter works
• Empty state updates when filter yields no results