feat: Enhance product support in Cart and OrderItem models

- Added new fields 'billing_cycle' and 'product_pricing_id' to Cart and OrderItem models.
- Updated product retrieval logic to support both new and legacy systems.
- Introduced relationships for Product and ProductPricings in Cart and OrderItem models.
- Created migration to add new fields to the carts and order_item tables.
- Updated frontend service index to handle new pricing structure and billing cycles.
- Improved UI components for better user experience in product selection and pricing display.
- Refactored action buttons in various views for consistency and improved styling.

app/Models/Os.php

@@ -39,4 +39,24 @@ class Os extends Model
                     ->withTimestamps()
                     ->withPivot('product_type');
     }
+
+    /**
+     * Many-to-many relationship với Products (new table: os_product)
+     */
+    public function products()
+    {
+        return $this->belongsToMany(\App\Models\Product::class, 'os_product', 'os_id', 'product_id')
+            ->withTimestamps();
+    }
+
+    /**
+     * Get display name with OS Group
+     */
+    public function getNameAttribute()
+    {
+        if ($this->osGroup) {
+            return $this->osGroup->name . ' ' . $this->version;
+        }
+        return $this->version;
+    }
 }