feat(graph): cut over chat diagnosis stategraph

src/main/resources/db/migration/V012__add_diagnosis_run_orchestration_trace.sql

@@ -0,0 +1,7 @@
+-- V012: add nullable StateGraph orchestration summary to diagnosis runs.
+-- Historical rows are intentionally not backfilled.
+
+ALTER TABLE diagnosis_run
+    ADD COLUMN orchestration_trace JSON NULL
+        COMMENT 'Compact run-scoped StateGraph orchestration summary'
+        AFTER self_evaluation;