feat: add Filament admin panel with migrations and design spec

- Add AdminPanelProvider mounting panel at `/admin` with `is_admin` auth guard
- Add `is_admin` boolean column to users table
- Add brent_prices and price_predictions tables with appropriate indexes
- Add comprehensive admin design spec covering resources, dashboard, navigation, and build order
- Configure default panel with amber primary color and standard middleware stack
- Add compiled Filament assets (actions.js, app.css)

.claude/rules/architecture.md

@@ -10,7 +10,7 @@ This keeps the app API-extractable later without a rewrite.
 
 ```
 app/
-├── Console/Commands/       # Scheduler commands (PollFuelPrices, RunScoringEngine)
+├── Console/Commands/       # Scheduler commands (PollFuelPrices, PredictOilPrices, RunScoringEngine)
 ├── Http/Controllers/       # Minimal — auth + Stripe webhook only
 ├── Livewire/               # Classic two-file Livewire components
 ├── Models/                 # Eloquent models
@@ -20,7 +20,11 @@ app/
 │   ├── AlertScoringService.php     # Fill-up timing recommendation engine
 │   ├── StationTaggingService.php   # Supermarket brand detection
 │   ├── NotificationDispatchService.php  # Tier-aware notification routing
-│   └── SubscriptionService.php    # Cashier/tier helpers
+│   ├── SubscriptionService.php    # Cashier/tier helpers
+│   ├── PostcodeService.php         # Resolves postcodes/outcodes/place names → lat/lng
+│   ├── OilPriceService.php         # FRED fetch + EWMA/LLM Brent crude prediction
+│   ├── LocationResult.php          # DTO returned by PostcodeService
+│   └── ApiLogger.php               # Wraps all outbound HTTP calls, logs to api_logs
 └── Jobs/                   # Queued jobs (dispatch notifications per user)
 
 resources/views/