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/Widgets/StatsOverviewWidget.php

@@ -47,7 +47,7 @@ class StatsOverviewWidget extends BaseWidget
 
     private function oilPredictionStat(): Stat
     {
-        $prediction = PricePrediction::latest('generated_at')->first();
+        $prediction = PricePrediction::bestFirst()->latest('generated_at')->first();
 
         if ($prediction === null) {
             return Stat::make('Latest oil prediction', 'None')