Filter counts update dynamically reflecting current filter intersection

Filter counts that show global totals instead of intersected totals (ISO 25010:2011 functional-suitability) actively mislead users. A user filtering by "Restaurants" who then sees "Rating: 4+ stars (847)" expects that number to reflect restaurants with high ratings — if it still reflects all 847 rated listings in the directory, they'll apply the filter expecting hundreds of results and land on a handful. This mismatch generates rage-clicks, support tickets, and abandoned sessions. The data contract between UI label and backend query must be exact: a count badge is a promise.

Expose a /api/listings/filter-counts endpoint that accepts all active filter params and returns counts scoped to their intersection. Call it every time the active filter set changes.

// /api/listings/filter-counts
export async function GET(req) {
  const category = req.nextUrl.searchParams.get('category')
  const baseWhere = { category } // extend with all active filters
  return Response.json({
    ratings: {
      '5': await countListings({ ...baseWhere, rating: 5 }),
      '4plus': await countListings({ ...baseWhere, rating: { gte: 4 } }),
    }
  })
}

On the frontend, trigger a refetch of filter counts inside the same effect that fires when any active filter changes, and update the displayed badge values from the response.