feat(phase-12): implement Red/Blue API endpoints (T-109, T-110, T-111, T-112)

T-109: Rewrite tests router with full Red/Blue workflow endpoints - list with filters, create from template, Red/Blue team updates with state guards, start-execution, submit-red, submit-blue, validate-red, validate-blue, reopen, and timeline. All using workflow service from Phase 11.

T-110: Rewrite evidence router with Red/Blue separation - upload with team field, list with team filter, delete with state-based permissions. Red Team edits in draft/red_executing, Blue Team in blue_evaluating, admin bypasses all.

T-111: Create test_templates router with full CRUD - paginated list with source/platform/severity/search filters, by-technique lookup, admin-only create/update, and soft delete. Registered in main.py.

T-112: Add POST /system/import-atomic-tests endpoint to system router - admin-only trigger for Atomic Red Team import with error handling and statistics response.

Includes validation tests for all four tasks (35 checks total).

backend/app/main.py

@@ -11,6 +11,7 @@ from app.routers import auth as auth_router
 from app.routers import techniques as techniques_router
 from app.routers import tests as tests_router
 from app.routers import evidence as evidence_router
+from app.routers import test_templates as test_templates_router
 from app.routers import system as system_router
 from app.routers import metrics as metrics_router
 from app.routers import users as users_router
@@ -50,6 +51,7 @@ app.include_router(auth_router.router, prefix="/api/v1")
 app.include_router(techniques_router.router, prefix="/api/v1")
 app.include_router(tests_router.router, prefix="/api/v1")
 app.include_router(evidence_router.router, prefix="/api/v1")
+app.include_router(test_templates_router.router, prefix="/api/v1")
 app.include_router(system_router.router, prefix="/api/v1")
 app.include_router(metrics_router.router, prefix="/api/v1")
 app.include_router(users_router.router, prefix="/api/v1")