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)

config/services.php

@@ -41,4 +41,13 @@ return [
         'client_secret' => env('FUEL_FINDER_CLIENT_SECRET'),
     ],
 
+    'fred' => [
+        'api_key' => env('FRED_API_KEY'),
+    ],
+
+    'anthropic' => [
+        'api_key' => env('ANTHROPIC_API_KEY'),
+        'model' => env('ANTHROPIC_MODEL', 'claude-haiku-4-5-20251001'),
+    ],
+
 ];