fix(graphql): skip client-side validation errors in error logging

GraphQL validation errors (unknown fields, syntax) have no
original_error — these are client mistakes, not server errors.
Skip them to avoid noisy Slack alerts.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ImTotem

src/bcsd_api/graphql/schema.py

@@ -59,6 +59,8 @@ class Mutation:
 class _Schema(strawberry.Schema):
     def process_errors(self, errors: List[GraphQLError], execution_context: ExecutionContext | None = None) -> None:
         for err in errors:
+            if not err.original_error:
+                continue
             if isinstance(err.original_error, AppException):
                 continue
             logger.error(err.message, exc_info=err.original_error)