feat(campaign): persist delivery execution mode

src/govoplan_campaign/backend/schemas.py

@@ -112,6 +112,8 @@ class CampaignVersionResponse(BaseModel):
     build_summary: dict[str, Any] | None = None
     execution_snapshot_hash: str | None = None
     execution_snapshot_at: datetime | None = None
+    delivery_mode: Literal["synchronous", "worker_queue", "database_queue"] | None = None
+    delivery_mode_selected_at: datetime | None = None
 
     @field_validator("editor_state", mode="before")
     @classmethod