feat: dashboard testing suite — scenario UI, load testing, dataset lineage

- 039-dashboard-scenario-ui: agent workspace (WorkspaceModel, scenario
  views, parameters/baselines, artifact preview, HITL save/approval,
  evidence/VLM review, pipeline verification views) + contextVersion=2
  scenario intent + prototype.
- 040-dashboard-load-testing: capacity/matrix/profile, runner pool,
  timing, circuit breaker, PROD gate, cache/bounded/consistency,
  comparison/schedule, API + frontend + prototype.
- 041-dataset-lineage-blast-radius: usage index, severity/schema-diff,
  propagation, deprecation, fanout, API + frontend + prototype (R9
  labels/metrics/recreate).
- 036/037 amendments: dataset_updated trigger + fanout_plan_id, lineage
  deprecation gate, 040 read-model traceability.
- Includes pre-existing 042-rls-management-workspace and
  043-idm-account-integration work.

backend/src/app.py

@@ -65,6 +65,8 @@ from .api.routes import (
     maintenance,
     mappings,
     migration,
+    lineage,
+    load_testing,
     plugins,
     profile,
     ready,
@@ -511,6 +513,8 @@ app.include_router(settings.router, prefix="/api/settings", tags=["Settings"])
 app.include_router(environments.router, tags=["Environments"])
 app.include_router(mappings.router, prefix="/api/mappings", tags=["Mappings"])
 app.include_router(migration.router)
+app.include_router(lineage.router)
+app.include_router(load_testing.router)
 app.include_router(git.router, prefix="/api/git", tags=["Git"])
 app.include_router(llm.router, prefix="/api/llm", tags=["LLM"])
 app.include_router(storage.router, prefix="/api/storage", tags=["Storage"])