Add Dagster orchestration and reduce active brands in backend

requirements-orchestration.txt

@@ -0,0 +1,20 @@
+# Dagster orchestration layer - DEVELOPMENT ONLY.
+#
+# Kept in a separate file from requirements.txt on purpose: the API image
+# (backend/Dockerfile) must not grow an orchestrator it never runs, and
+# docker-compose.prod.yml already allocates the whole 8GB VPS (ollama 3G,
+# backend 2560M, postgres 1G) with no headroom for a daemon + webserver.
+#
+#   pip install -r requirements-orchestration.txt
+#   dagster dev -m orchestration.definitions -p 3030      (run from backend/)
+#
+# Compatibility notes:
+#  * dagster 1.13 declares requires_python <3.15,>=3.10, so the local 3.14
+#    interpreter and the container's 3.11 are both supported.
+#  * dagster pins protobuf<7 while the ambient environment has 7.x. Installing
+#    into backend/venv shadows it for this project only.
+#  * dagster-postgres is deliberately NOT used - it needs psycopg2-binary and
+#    this project is on psycopg3. Run/event storage stays on the default
+#    SQLite instance under orchestration/.dagster_home.
+dagster>=1.13,<1.14
+dagster-webserver>=1.13,<1.14