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)

composer.json

@@ -3,13 +3,11 @@
     "name": "laravel/livewire-starter-kit",
     "type": "project",
     "description": "The official Laravel starter kit for Livewire.",
-    "keywords": [
-        "laravel",
-        "framework"
-    ],
+    "keywords": ["laravel", "framework"],
     "license": "MIT",
     "require": {
         "php": "^8.3",
+        "filament/filament": "^5.0",
         "laravel/fortify": "^1.34",
         "laravel/framework": "^13.0",
         "laravel/tinker": "^3.0",
@@ -69,7 +67,8 @@
         ],
         "post-autoload-dump": [
             "Illuminate\\Foundation\\ComposerScripts::postAutoloadDump",
-            "@php artisan package:discover --ansi"
+            "@php artisan package:discover --ansi",
+            "@php artisan filament:upgrade"
         ],
         "post-update-cmd": [
             "@php artisan vendor:publish --tag=laravel-assets --ansi --force"