feat: add empty extras markers for cloud/notification integrations (Phase 1)

Co-Authored-By: Itamar Hartstein <haritamar@gmail.com>

Author: devin-ai-integration[bot]

pyproject.toml

@@ -82,6 +82,14 @@ fabricspark = ["dbt-fabricspark"]
 sqlserver = ["dbt-sqlserver"]
 vertica = ["dbt-vertica"]
 
+# Cloud storage and notification extras (Phase 1: empty, deps are still required).
+# In Phase 2 these will reference the actual optional dependencies.
+s3 = []
+gcs = []
+azure = []
+slack = []
+teams = []
+
 # dbt-fabricspark is excluded due to broken upstream dependencies (azure-cli pre-release pins).
 # dbt-vertica is excluded because it pins dbt-core==1.8.5, forcing the entire resolution to dbt 1.8.
 # Both are still available as individual extras (e.g. pip install elementary-data[vertica]).