feat(campaign): enforce attachment delivery policies

src/govoplan_campaign/backend/campaign/models.py

@@ -404,11 +404,20 @@ class AttachmentsConfig(StrictModel):
     base_paths: list[AttachmentBasePathConfig] = Field(default_factory=list)
     allow_individual: bool = False
     send_without_attachments: bool = True
+    send_without_attachments_behavior: Behavior | None = None
     zip: ZipCollectionConfig = Field(default_factory=ZipCollectionConfig)
     global_: list[AttachmentConfig] = Field(default_factory=list, alias="global")
     missing_behavior: Behavior = Behavior.ASK
     ambiguous_behavior: Behavior = Behavior.ASK
 
+    @model_validator(mode="after")
+    def normalize_send_without_attachments_behavior(self) -> "AttachmentsConfig":
+        if self.send_without_attachments_behavior is None:
+            self.send_without_attachments_behavior = Behavior.CONTINUE if self.send_without_attachments else Behavior.BLOCK
+        else:
+            self.send_without_attachments = self.send_without_attachments_behavior != Behavior.BLOCK
+        return self
+
     @property
     def individual_base_path_values(self) -> set[str]:
         return {base_path.path for base_path in self.base_paths if base_path.allow_individual}