✨(backend) add ai_proxy

Add AI proxy to handle AI related requests
to the AI service.

src/backend/core/api/serializers.py

@@ -833,6 +833,41 @@ class AITranslateSerializer(serializers.Serializer):
         return value
 
 
+class AIProxySerializer(serializers.Serializer):
+    """Serializer for AI proxy requests."""
+
+    messages = serializers.ListField(
+        required=True,
+        child=serializers.DictField(
+            child=serializers.CharField(required=True),
+        ),
+        allow_empty=False,
+    )
+    model = serializers.CharField(required=True)
+
+    def validate_messages(self, messages):
+        """Validate messages structure."""
+        # Ensure each message has the required fields
+        for message in messages:
+            if (
+                not isinstance(message, dict)
+                or "role" not in message
+                or "content" not in message
+            ):
+                raise serializers.ValidationError(
+                    "Each message must have 'role' and 'content' fields"
+                )
+
+        return messages
+
+    def validate_model(self, value):
+        """Validate model value is the same than settings.AI_MODEL"""
+        if value != settings.AI_MODEL:
+            raise serializers.ValidationError(f"{value} is not a valid model")
+
+        return value
+
+
 class MoveDocumentSerializer(serializers.Serializer):
     """
     Serializer for validating input data to move a document within the tree structure.