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

tests/Feature/Payments/BillingControllerTest.php

@@ -0,0 +1,57 @@
+<?php
+
+use App\Models\User;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+
+uses(RefreshDatabase::class);
+
+beforeEach(function (): void {
+    config([
+        'services.stripe.prices.basic.monthly' => 'price_test_basic_monthly',
+        'services.stripe.prices.basic.annual' => 'price_test_basic_annual',
+        'services.stripe.prices.plus.monthly' => 'price_test_plus_monthly',
+        'services.stripe.prices.plus.annual' => 'price_test_plus_annual',
+        'services.stripe.prices.pro.monthly' => null,
+        'services.stripe.prices.pro.annual' => null,
+    ]);
+});
+
+it('requires authentication for the checkout route', function (): void {
+    $this->get('/billing/checkout/basic/monthly')->assertRedirect('/login');
+});
+
+it('requires authentication for the portal route', function (): void {
+    $this->get('/billing/portal')->assertRedirect('/login');
+});
+
+it('rejects an unknown tier', function (): void {
+    $this->actingAs(User::factory()->create())
+        ->get('/billing/checkout/titanium/monthly')
+        ->assertNotFound();
+});
+
+it('rejects an unknown cadence', function (): void {
+    $this->actingAs(User::factory()->create())
+        ->get('/billing/checkout/basic/weekly')
+        ->assertNotFound();
+});
+
+it('returns 404 when no price is configured for the tier + cadence', function (): void {
+    $this->actingAs(User::factory()->create())
+        ->get('/billing/checkout/pro/monthly')
+        ->assertNotFound();
+});
+
+it('redirects the success route to the dashboard', function (): void {
+    $this->actingAs(User::factory()->create())
+        ->get('/billing/success')
+        ->assertRedirect(route('dashboard'))
+        ->assertSessionHas('status', 'subscription_started');
+});
+
+it('redirects the cancel route to the dashboard', function (): void {
+    $this->actingAs(User::factory()->create())
+        ->get('/billing/cancel')
+        ->assertRedirect(route('dashboard'))
+        ->assertSessionHas('status', 'subscription_cancelled');
+});