Skip self-dependencies in dependency resolver

PyPI packages can have self-referential dependencies for extras
(e.g., pytest[testing] depends on pytest). These were incorrectly
detected as circular dependencies. Now we skip them.

backend/app/dependencies.py

@@ -767,6 +767,10 @@ def resolve_dependencies(
 
         # Resolve each dependency first (depth-first)
         for dep in deps:
+            # Skip self-dependencies (can happen with PyPI extras like pytest[testing])
+            if dep.dependency_project == proj_name and dep.dependency_package == pkg_name:
+                continue
+
             resolved_dep = _resolve_dependency_to_artifact(
                 db,
                 dep.dependency_project,