Add fuel API ingestion and historic storage design spec

Includes verified API authentication flow, correct base URL, all DB
table schemas for stations, current prices, history, and archive.
Fuel types corrected to match live API (B7_STANDARD, B7_PREMIUM).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.claude/rules/testing.md

@@ -0,0 +1,48 @@
+# Testing
+
+## Framework
+
+Pest PHP. Never use PHPUnit test classes directly — always Pest syntax.
+
+## Test structure
+
+```
+tests/
+├── Feature/
+│   ├── Scoring/AlertScoringServiceTest.php
+│   ├── Notifications/NotificationDispatchTest.php
+│   ├── Payments/SubscriptionTest.php
+│   └── Livewire/DashboardTest.php
+└── Unit/
+    ├── Services/FuelPriceServiceTest.php
+    └── Services/StationTaggingServiceTest.php
+```
+
+## Conventions
+
+- Use `RefreshDatabase` trait on Feature tests
+- Factory-first: all test data via Eloquent factories — never raw DB inserts
+- Mock external APIs (Fuel Finder, Vonage, OneSignal, FRED) — never hit live APIs in tests
+- Use `Http::fake()` for all outbound HTTP in tests
+- Stripe: use Cashier's built-in test helpers, never hit Stripe API in tests
+
+## What to test
+
+- AlertScoringService: all signal combinations, confidence thresholds, no_signal cases
+- NotificationDispatchService: correct channels returned per tier
+- SubscriptionService: tier detection, SMS limit counting
+- Livewire components: use `Livewire::test()` for interaction testing
+- Stripe webhooks: test `customer.subscription.deleted` downgrades user correctly
+
+## Running tests
+
+```bash
+php artisan test              # Full suite
+php artisan test --filter=Scoring  # Single test class
+php artisan test --parallel   # Parallel (faster)
+```
+
+---
+paths:
+  - "tests/**/*.php"
+---