feat(d3fend): flag review_required on new ATT&CK-D3FEND mappings

Mirrors the existing Atomic/Caldera/Elastic/Sigma/LOLBAS import pattern —
D3FEND mapping import was the one source silently skipping the
review_required flag, so leads never got prompted to review techniques
that only gained new D3FEND coverage.

backend/app/services/d3fend_import_service.py

@@ -583,6 +583,8 @@ def import_d3fend_mappings(db: Session) -> dict[str, int]:
     created = 0
     # Assign skipped = 0
     skipped = 0
+    # Assign new_technique_ids = set()
+    new_technique_ids: set[str] = set()
 
     # Get all ATT&CK techniques from the DB
     attack_techniques = db.query(Technique).all()
@@ -649,6 +651,12 @@ def import_d3fend_mappings(db: Session) -> dict[str, int]:
             db.add(mapping)
             # Assign created = 1
             created += 1
+            new_technique_ids.add(mitre_id)
+
+    if new_technique_ids:
+        db.query(Technique).filter(
+            Technique.mitre_id.in_(new_technique_ids)
+        ).update({"review_required": True}, synchronize_session=False)
 
     # Commit all pending changes to the database
     db.commit()