feat: normalize and validate checkpoint entries before enrichment

Add _normalize_checkpoint_entry method to handle legacy checkpoint data formats (strings, tuples) by converting them to dictionaries. This prevents errors during enrichment when checkpoint data is not in the expected dictionary format. Invalid checkpoint entries are now removed instead of causing processing failures.

- Update get_paginated_data and get_recipe_by_id methods to use normalization
- Add test cases for legacy string and tuple checkpoint formats
- Ensure backward compatibility with existing checkpoint handling

py/services/recipe_scanner.py

@@ -949,7 +949,11 @@ class RecipeScanner:
             if 'loras' in item:
                 item['loras'] = [self._enrich_lora_entry(dict(lora)) for lora in item['loras']]
             if item.get('checkpoint'):
-                item['checkpoint'] = self._enrich_checkpoint_entry(dict(item['checkpoint']))
+                checkpoint_entry = self._normalize_checkpoint_entry(item['checkpoint'])
+                if checkpoint_entry:
+                    item['checkpoint'] = self._enrich_checkpoint_entry(checkpoint_entry)
+                else:
+                    item.pop('checkpoint', None)
 
         result = {
             'items': paginated_items,
@@ -998,7 +1002,11 @@ class RecipeScanner:
         if 'loras' in formatted_recipe:
             formatted_recipe['loras'] = [self._enrich_lora_entry(dict(lora)) for lora in formatted_recipe['loras']]
         if formatted_recipe.get('checkpoint'):
-            formatted_recipe['checkpoint'] = self._enrich_checkpoint_entry(dict(formatted_recipe['checkpoint']))
+            checkpoint_entry = self._normalize_checkpoint_entry(formatted_recipe['checkpoint'])
+            if checkpoint_entry:
+                formatted_recipe['checkpoint'] = self._enrich_checkpoint_entry(checkpoint_entry)
+            else:
+                formatted_recipe.pop('checkpoint', None)
 
         return formatted_recipe