schema clean up and refactor

core/schema/serializers/__init__.py

@@ -0,0 +1,11 @@
+"""
+Model serializers — one module per model group, mirroring core/schema/models/.
+
+    models/detect_pipeline.py  → serializers/detect_pipeline.py
+    models/detect_jobs.py      → serializers/detect_jobs.py
+    models/detect.py           → serializers/detect.py (SSE events)
+
+Common utilities in _common.py.
+"""
+
+from ._common import safe_construct, serialize_dataclass, serialize_dataclass_list