Add tier feature design spec, annual billing, fuel type normalization, and admin subscription management

- Add comprehensive tier feature matrix spec defining Free/Basic/Plus/Pro capabilities across recommendations, predictions, history, logs, tools, and family sharing
- Add `stripe_price_id_annual` column to plans table and rename existing column to `stripe_price_id_monthly`
- Normalize legacy fuel type aliases (petrol→e10, diesel→b7_standard) in users table
- Implement BillingController with checkout, portal, success/cancel routes supporting monthly/annual cadence
- Add admin subscription assignment in Filament user edit page with admin-granted subscription support
- Add DowngradeUserOnSubscriptionDeleted listener to disable WhatsApp/SMS preferences on subscription cancellation
- Add MissedNotificationsOverview widget to Filament user detail page
- Add PollFuelPricesTest covering auto-refresh scenarios
- Add PriceReliability enum with reliability classification based on price age
- Add fuelTypes.js constants file exporting FUEL_TYPES from window global

app/Enums/PriceReliability.php

@@ -0,0 +1,45 @@
+<?php
+
+namespace App\Enums;
+
+use Illuminate\Support\Carbon;
+
+enum PriceReliability: string
+{
+    case Reliable = 'reliable';
+    case Stale = 'stale';
+    case Outdated = 'outdated';
+
+    public static function fromUpdatedAt(?Carbon $updatedAt): self
+    {
+        if ($updatedAt === null) {
+            return self::Outdated;
+        }
+
+        $hours = $updatedAt->diffInHours(now());
+
+        return match (true) {
+            $hours <= 72 => self::Reliable,
+            $hours <= 168 => self::Stale,
+            default => self::Outdated,
+        };
+    }
+
+    public function weight(): int
+    {
+        return match ($this) {
+            self::Reliable => 0,
+            self::Stale => 1,
+            self::Outdated => 2,
+        };
+    }
+
+    public function label(): string
+    {
+        return match ($this) {
+            self::Reliable => 'Reliable',
+            self::Stale => 'Older price — verify before driving',
+            self::Outdated => 'Outdated — may be inaccurate',
+        };
+    }
+}