feat(knowledge): Phase 11 — Knowledge Management (Playbooks + Lessons Learned) [FASE-11]

- Playbooks: versioned Markdown runbooks per technique × type (attack/detect/investigate/respond/hunt)
- PlaybookVersion: immutable snapshots on every update; restore to any previous version
- LessonLearned: post-mortem records linked to tests/campaigns/attack-paths or manual
- Alembic migration b037know (raw SQL, idempotent, no PostgreSQL enums)
- Router /api/v1/knowledge: 14 endpoints for playbooks + lessons + stats
- Pydantic validators for playbook_type, severity, entity_type (422 on invalid)
- Knowledge stats endpoint: totals + breakdown by severity and playbook type
- Soft-delete on both resources; include_inactive filter for admin recovery
- QA script: 70+ tests across CRUD, versioning, filtering, auth, soft-delete, regression

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

backend/app/models/__init__.py

@@ -38,6 +38,7 @@ from app.models.attack_path import (
     AttackPathStepResult, TimelineEntry,
     ExecutionStatus, StepResultStatus, TimelineActorSide, TimelineEntryType,
 )
+from app.models.knowledge import Playbook, PlaybookVersion, LessonLearned
 
 __all__ = [
     "User", "Technique", "Test", "TestTemplate", "Evidence",
@@ -59,4 +60,5 @@ __all__ = [
     "AttackPath", "AttackPathStep", "AttackPathExecution",
     "AttackPathStepResult", "TimelineEntry",
     "ExecutionStatus", "StepResultStatus", "TimelineActorSide", "TimelineEntryType",
+    "Playbook", "PlaybookVersion", "LessonLearned",
 ]