feat(backend): sprint 5 — SimulationTemplate CRUD + instantiation

- SimulationTemplate model + migration 0005 (CREATE TABLE + name index)
- 5 CRUD endpoints under /api/templates (admin|redteam only, SOC 403)
- POST /api/engagements/<eid>/simulations extended with optional template_id
- serialize_template() reusing _enrich_techniques/_enrich_tactics helpers
- IntegrityError → 409 for duplicate name on both POST and PATCH
- 28 new tests (CRUD, RBAC, dedup, instantiation, migration round-trip)
- 221 tests pass; ruff clean; mypy clean

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

backend/app/__init__.py

@@ -6,7 +6,7 @@ from pathlib import Path
 
 from flask import Flask, jsonify, send_from_directory
 
-from backend.app.api import auth_bp, engagements_bp, simulations_bp, users_bp
+from backend.app.api import auth_bp, engagements_bp, simulations_bp, templates_bp, users_bp
 from backend.app.cli import register_cli
 from backend.app.config import Config, TestConfig
 from backend.app.errors import register_error_handlers
@@ -37,6 +37,7 @@ def create_app(config_object: object | None = None) -> Flask:
     app.register_blueprint(users_bp)
     app.register_blueprint(engagements_bp)
     app.register_blueprint(simulations_bp)
+    app.register_blueprint(templates_bp)
 
     from backend.app.services import mitre as mitre_svc
     mitre_svc.load_bundle()