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/Providers/AppServiceProvider.php

@@ -59,13 +59,6 @@ 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()