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>

app/Filament/Resources/Searches/Pages/ListSearches.php

@@ -0,0 +1,16 @@
+<?php
+
+namespace App\Filament\Resources\Searches\Pages;
+
+use App\Filament\Resources\Searches\SearchResource;
+use Filament\Resources\Pages\ListRecords;
+
+class ListSearches extends ListRecords
+{
+    protected static string $resource = SearchResource::class;
+
+    protected function getHeaderActions(): array
+    {
+        return [];
+    }
+}