feat(cms): implement complete SysSiteCMS content management system

Initial implementation of the HomeSysPanel CMS built with Laravel 13.0.
Includes complete admin panel, content management, user authentication,
modular architecture for products/services/chatbot, and marketing tools.

Key features:
- User authentication with email verification and password reset
- Role-based access control (Admin/User with granular permissions)
- Content management (pages, news, FAQ, downloads, galleries, banners)
- Contact management system with subjects and responses
- Marketing tools (email campaigns, visitor analytics, social sharing)
- Modular architecture (Products, Services, Chatbot modules)
- AI Chatbot integration with OpenRouter.ai and LlamaCpp support
- Visitor tracking with geolocation
- SEO optimization with meta tags and Open Graph
- Responsive design with Bootstrap 5
- Dark mode support
- Maintenance mode
- Feature request system

app/Models/Setting.php

@@ -0,0 +1,21 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Model;
+
+class Setting extends Model
+{
+    protected $fillable = ['key', 'value', 'group'];
+
+    public static function get($key, $default = null)
+    {
+        $setting = self::where('key', $key)->first();
+        return ($setting && $setting->value !== '' && $setting->value !== null) ? $setting->value : $default;
+    }
+
+    public static function set($key, $value, $group = 'general')
+    {
+        return self::updateOrCreate(['key' => $key], ['value' => $value, 'group' => $group]);
+    }
+}