Add description field to Product model

Issue: The landing page template supported displaying product descriptions,
but the Product model didn't load the description field from config.yaml files.

Changes:
- Added optional 'description' parameter to Product.__init__()
- Updated Product.to_dict() to include description (if present)
- Updated Product.from_dict() to load description from config
- Added test to verify descriptions are displayed on landing page

All 9 landing page tests passing.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/models/product.py

@@ -14,16 +14,18 @@ class Product:
         owner_language: Preferred language for product owner
         assigned_owner_ids: List of product owner user IDs
         status: Product status ('active' or 'archived')
+        description: Optional product description for landing page
     """
 
     def __init__(self, product_id, name, submission_url_slug, owner_language,
-                 assigned_owner_ids, status='active'):
+                 assigned_owner_ids, status='active', description=None):
         self.product_id = product_id
         self.name = name
         self.submission_url_slug = submission_url_slug
         self.owner_language = owner_language
         self.assigned_owner_ids = assigned_owner_ids or []
         self.status = status
+        self.description = description
 
     def to_dict(self):
         """Convert product to dictionary
@@ -31,7 +33,7 @@ class Product:
         Returns:
             dict: Product data
         """
-        return {
+        data = {
             'product_id': self.product_id,
             'name': self.name,
             'submission_url_slug': self.submission_url_slug,
@@ -39,6 +41,9 @@ class Product:
             'assigned_owner_ids': self.assigned_owner_ids,
             'status': self.status
         }
+        if self.description:
+            data['description'] = self.description
+        return data
 
     @classmethod
     def from_dict(cls, data):
@@ -56,7 +61,8 @@ class Product:
             submission_url_slug=data['submission_url_slug'],
             owner_language=data['owner_language'],
             assigned_owner_ids=data.get('assigned_owner_ids', []),
-            status=data.get('status', 'active')
+            status=data.get('status', 'active'),
+            description=data.get('description')
         )
 
     @staticmethod