chore: audit nits — PlanFeatures, test boot, EIA log, static method

Audit items #15, #16, #20, #22.

#15 — AuthController::me and UserResource form/table now read tier via
PlanFeatures::for($user)->tier() instead of Plan::resolveForUser($user)
->name. Tiers.md: PlanFeatures is the single entitlement gate.

#16 — Moved SQLite GREATEST/LEAST PHP-backed function registration from
AppServiceProvider::boot to tests/TestCase::setUp. Production app boot no
longer checks the DB driver name.

#20 — FetchOilPrices: added Log::warning on EIA fallback and Log::error
on both-providers-failed so primary-source reliability can be trended
beyond the cron output buffer.

#22 — FuelPriceService::flattenEnabledFlags is now an instance method,
matching the rest of the class. No external callers.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/Http/Controllers/Api/AuthController.php

@@ -5,6 +5,7 @@ namespace App\Http\Controllers\Api;
 use App\Http\Controllers\Controller;
 use App\Models\Plan;
 use App\Models\User;
+use App\Services\PlanFeatures;
 use Illuminate\Http\JsonResponse;
 use Illuminate\Http\Request;
 use Illuminate\Support\Facades\Auth;
@@ -70,7 +71,7 @@ class AuthController extends Controller
         return response()->json(array_merge(
             $user->toArray(),
             [
-                'tier' => Plan::resolveForUser($user)->name,
+                'tier' => PlanFeatures::for($user)->tier(),
                 'subscription_cancelled' => $subscription?->canceled() ?? false,
                 'subscription_cadence' => Plan::resolveCadenceForUser($user),
                 'subscribed_at' => $subscription?->created_at?->toIso8601String(),