feat(pipeline): G1 Decision Trace — compliance decision tracking

New table: decision_traces (status, reason, evidence, fix plan per control)
New API:
  POST/GET/PUT /v1/decision-traces (CRUD for decisions)
  GET /v1/decision-traces/stats (compliance dashboard)
  GET /v1/controls/{id}/full-trace (Regulation→Obligation→Control→Decision→Evidence)

454 tests pass, 0 regressions.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

control-pipeline/api/__init__.py

@@ -5,6 +5,8 @@ from api.canonical_control_routes import router as canonical_router
 from api.document_compliance_routes import router as document_router
 from api.dependency_routes import router as dependency_router
 from api.master_control_routes import router as master_control_router
+from api.decision_trace_routes import router as decision_trace_router
+from api.decision_trace_routes import full_trace_router
 
 router = APIRouter()
 router.include_router(generator_router)
@@ -12,3 +14,5 @@ router.include_router(canonical_router)
 router.include_router(document_router)
 router.include_router(dependency_router)
 router.include_router(master_control_router)
+router.include_router(decision_trace_router)
+router.include_router(full_trace_router)