feat: FuelPriceService with OAuth token caching

Also extend Pest TestCase to Unit tests and guard MySQL-only migration
DDL (composite PK + PARTITION BY) behind a driver check so in-memory
SQLite tests can run migrations cleanly.

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

app/Services/FuelPriceService.php

@@ -0,0 +1,28 @@
+<?php
+
+namespace App\Services;
+
+use Illuminate\Support\Facades\Cache;
+use Illuminate\Support\Facades\Http;
+
+class FuelPriceService
+{
+    private const TOKEN_CACHE_KEY = 'fuel_finder_access_token';
+
+    public function __construct(
+        private readonly StationTaggingService $taggingService,
+    ) {}
+
+    public function getAccessToken(): string
+    {
+        return Cache::remember(self::TOKEN_CACHE_KEY, 3540, function (): string {
+            $response = Http::timeout(10)
+                ->post(config('services.fuel_finder.base_url').'/oauth/generate_access_token', [
+                    'client_id'     => config('services.fuel_finder.client_id'),
+                    'client_secret' => config('services.fuel_finder.client_secret'),
+                ]);
+
+            return $response->json('data.access_token');
+        });
+    }
+}