refactor(core): introduce Unit of Work and remove commits from services

- Add UnitOfWork context manager in domain/unit_of_work.py with commit/rollback/flush API and auto-rollback on exception

- Remove all db.commit() from test_workflow_service (8 calls), notification_service (4 calls), status_service (1 call)

- Services now only stage changes via db.add/db.flush; caller owns the transaction boundary

- Update routers/tests.py: wrap 9 workflow endpoints in UnitOfWork context managers

- Update routers/notifications.py: wrap mark_as_read and mark_all_as_read in UnitOfWork

backend/app/services/status_service.py

@@ -4,6 +4,9 @@ based on the state and result of its associated tests.
 V2 rules account for dual Red/Blue validation and use
 ``detection_result`` (filled by Blue Team) instead of the legacy
 ``result`` field.
+
+This function mutates the technique but does **not** commit.
+The caller is responsible for committing the session.
 """
 
 from sqlalchemy.orm import Session
@@ -42,5 +45,3 @@ def recalculate_technique_status(db: Session, technique: Technique) -> None:
         technique.status_global = TechniqueStatus.partial
     else:
         technique.status_global = TechniqueStatus.in_progress
-
-    db.commit()