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/models/__init__.py

@@ -23,6 +23,12 @@ from app.models.scoring_config import ScoringConfig
 from app.models.enums import TechniqueStatus, TestState, TestResult, TeamSide
 from app.models.webhook_config import WebhookConfig
 from app.models.system_config import SystemConfig
+from app.models.detection_lifecycle import (
+    DetectionAsset, DetectionTechniqueMapping, DetectionValidation,
+    TechniqueConfidenceScore, InfrastructureChangeLog,
+    DetectionConfidence, DetectionHealthStatus, InvalidationReason,
+)
+from app.models.decay_policy import DecayPolicy
 
 __all__ = [
     "User", "Technique", "Test", "TestTemplate", "Evidence",
@@ -37,4 +43,6 @@ __all__ = [
     "Worklog", "OsintItem", "ScoringConfig",
     "TechniqueStatus", "TestState", "TestResult", "TeamSide",
     "WebhookConfig", "SystemConfig",
+    "DetectionAsset", "DetectionTechniqueMapping", "DetectionValidation",
+    "TechniqueConfidenceScore", "InfrastructureChangeLog", "DecayPolicy",
 ]