feat(dlm): Phase 8 — Detection Lifecycle Management [FASE-8]

Tasks 8.1-8.5:

Models (8.1):
- DetectionAsset: SIEM/EDR/Sigma rule assets with auto-hash
- DetectionTechniqueMapping: N:M asset ↔ technique coverage
- DetectionValidation: immutable validation records with expiry
- TechniqueConfidenceScore: computed multi-factor confidence
- InfrastructureChangeLog: infra changes that invalidate detections
- DecayPolicy: configurable freshness thresholds per platform/tactic

Services (8.2, 8.3):
- detection_asset_service: CRUD + SHA-256 rule hashing + auto-
  invalidation on rule/infra changes
- decay_engine_service: daily decay engine — expires stale validations,
  recalculates confidence (recency/coverage/health/diversity factors),
  processes infrastructure change propagation

Router (8.4): 15 endpoints under /api/v1/detection-lifecycle:
  assets CRUD, technique mappings, validations, confidence scores,
  infrastructure changes, decay trigger, executive dashboard

Scheduler (8.3): decay engine runs daily at 02:00
Seed (8.5): default policy (90/180/365d) + strict initial-access policy
Migration: b034dlm (6 tables, 11 indexes)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/main.py

@@ -38,6 +38,7 @@ from app.routers import analytics as analytics_router
 from app.routers import advanced_metrics as advanced_metrics_router
 from app.routers import osint as osint_router
 from app.routers import webhooks as webhooks_router
+from app.routers import detection_lifecycle as detection_lifecycle_router
 from app.domain.errors import DomainError
 from app.middleware.error_handler import domain_exception_handler
 from app.middleware.request_context import RequestContextMiddleware
@@ -58,6 +59,16 @@ async def lifespan(app: FastAPI):
     """Startup / shutdown logic."""
     ensure_bucket_exists()
     start_scheduler()
+    # Seed decay policies
+    from app.database import SessionLocal
+    from app.seed_decay_policies import seed_decay_policies
+    db = SessionLocal()
+    try:
+        seed_decay_policies(db)
+    except Exception:
+        pass
+    finally:
+        db.close()
     yield
     # Graceful shutdown of the background scheduler
     scheduler.shutdown(wait=False)
@@ -125,6 +136,7 @@ app.include_router(analytics_router.router, prefix="/api/v1")
 app.include_router(advanced_metrics_router.router, prefix="/api/v1")
 app.include_router(osint_router.router, prefix="/api/v1")
 app.include_router(webhooks_router.router, prefix="/api/v1")
+app.include_router(detection_lifecycle_router.router, prefix="/api/v1")
 
 
 @app.get("/health", include_in_schema=False)