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/Console/Commands/FetchOilPrices.php

@@ -7,6 +7,7 @@ use App\Services\BrentPriceSources\BrentPriceFetchException;
 use Illuminate\Console\Attributes\Description;
 use Illuminate\Console\Attributes\Signature;
 use Illuminate\Console\Command;
+use Illuminate\Support\Facades\Log;
 
 #[Signature('oil:fetch')]
 #[Description('Fetch latest Brent crude prices (EIA primary, FRED fallback)')]
@@ -20,6 +21,7 @@ class FetchOilPrices extends Command
 
             return self::SUCCESS;
         } catch (BrentPriceFetchException $e) {
+            Log::warning('FetchOilPrices: EIA fetch failed, falling back to FRED', ['error' => $e->getMessage()]);
             $this->warn('EIA fetch failed: '.$e->getMessage().'. Trying FRED...');
         }
 
@@ -29,6 +31,7 @@ class FetchOilPrices extends Command
 
             return self::SUCCESS;
         } catch (BrentPriceFetchException $e) {
+            Log::error('FetchOilPrices: both EIA and FRED failed', ['error' => $e->getMessage()]);
             $this->error('Both EIA and FRED failed: '.$e->getMessage());
 
             return self::FAILURE;