feat: add updated and brand sort options to /api/stations endpoint

Extends NearbyStationsRequest validation to accept `sort=updated` and `sort=brand`. Updates StationController to use match expression with dedicated closures: 'updated' sorts by price_effective_at descending (newest first), 'brand' sorts alphabetically by brand_name, with existing price and distance options.

app/Http/Controllers/Api/StationController.php

@@ -54,7 +54,12 @@ class StationController extends Controller
 
         $stations = $all
             ->filter(fn ($s) => (float) $s->distance_km <= $radius)
-            ->sortBy($sort === 'price' ? 'price_pence' : 'distance_km')
+            ->sortBy(match ($sort) {
+                'price' => fn ($s) => (int) $s->price_pence,
+                'updated' => fn ($s) => $s->price_effective_at ? -strtotime($s->price_effective_at) : PHP_INT_MAX,
+                'brand' => fn ($s) => strtolower((string) $s->brand_name),
+                default => fn ($s) => (float) $s->distance_km,
+            })
             ->values();
 
         $prices = $stations->pluck('price_pence');