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/Providers/AppServiceProvider.php

@@ -37,6 +37,13 @@ class AppServiceProvider extends ServiceProvider
             app()->isProduction(),
         );
 
+        // SQLite lacks GREATEST/LEAST scalar functions — register them for tests.
+        if (DB::connection()->getDriverName() === 'sqlite') {
+            $pdo = DB::connection()->getPdo();
+            $pdo->sqliteCreateFunction('GREATEST', fn (...$args) => max($args), -1);
+            $pdo->sqliteCreateFunction('LEAST', fn (...$args) => min($args), -1);
+        }
+
         Password::defaults(fn (): ?Password => app()->isProduction()
             ? Password::min(12)
                 ->mixedCase()