feat: add postcode resolution to /api/stations and Filament SearchResource

Extends NearbyStationsRequest to accept `postcode` (full or outcode) as an alternative to lat/lng. PostcodeService resolves it via postcodes.io and falls through to coordinates. Also adds SearchResource to the Filament admin panel for viewing logged search activity with fuel type filter and price/distance stats columns. Includes SQLite GREATEST/LEAST function polyfills in AppServiceProvider for test compatibility.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/Feature/Api/StationControllerTest.php

@@ -4,6 +4,7 @@ use App\Enums\FuelType;
 use App\Models\Station;
 use App\Models\StationPriceCurrent;
 use Illuminate\Foundation\Testing\RefreshDatabase;
+use Illuminate\Support\Facades\Http;
 
 uses(RefreshDatabase::class);
 
@@ -102,3 +103,53 @@ it('returns 422 when required params are missing', function () {
     $this->getJson('/api/stations?lat=52.5')
         ->assertUnprocessable();
 });
+
+it('resolves a full postcode to coordinates and returns nearby stations', function () {
+    $station = Station::factory()->create(['lat' => 51.5010, 'lng' => -0.1415]);
+    StationPriceCurrent::factory()->create([
+        'station_id' => $station->node_id,
+        'fuel_type' => FuelType::E10,
+        'price_pence' => 14200,
+    ]);
+
+    Http::fake([
+        'api.postcodes.io/postcodes/SW1A1AA' => Http::response([
+            'status' => 200,
+            'result' => ['postcode' => 'SW1A 1AA', 'latitude' => 51.5010, 'longitude' => -0.1415],
+        ]),
+    ]);
+
+    $this->getJson('/api/stations?postcode=SW1A+1AA&fuel_type=e10&radius=1')
+        ->assertOk()
+        ->assertJsonPath('meta.count', 1);
+});
+
+it('resolves an outcode to coordinates', function () {
+    $station = Station::factory()->create(['lat' => 51.5010, 'lng' => -0.1415]);
+    StationPriceCurrent::factory()->create([
+        'station_id' => $station->node_id,
+        'fuel_type' => FuelType::E10,
+        'price_pence' => 14200,
+    ]);
+
+    Http::fake([
+        'api.postcodes.io/outcodes/SW1A' => Http::response([
+            'status' => 200,
+            'result' => ['outcode' => 'SW1A', 'latitude' => 51.5010, 'longitude' => -0.1415],
+        ]),
+    ]);
+
+    $this->getJson('/api/stations?postcode=SW1A&fuel_type=e10&radius=1')
+        ->assertOk()
+        ->assertJsonPath('meta.count', 1);
+});
+
+it('returns 422 when postcode cannot be resolved', function () {
+    Http::fake([
+        'api.postcodes.io/*' => Http::response(['status' => 404, 'error' => 'Postcode not found'], 404),
+    ]);
+
+    $this->getJson('/api/stations?postcode=ZZ99+9ZZ&fuel_type=e10')
+        ->assertUnprocessable()
+        ->assertJsonValidationErrors(['postcode']);
+});