feat: add campaign copying scheduling and residual handling

src/govoplan_campaign/backend/schema/campaign.schema.json

@@ -371,6 +371,9 @@
             "warn"
           ],
           "default": "ask"
+        },
+        "residual_files": {
+          "$ref": "#/$defs/residual_file_disposition"
         }
       },
       "additionalProperties": false,
@@ -1455,6 +1458,34 @@
       },
       "additionalProperties": false
     },
+    "residual_file_disposition": {
+      "type": "object",
+      "properties": {
+        "mode": {
+          "type": "string",
+          "enum": ["none", "report", "attach"],
+          "default": "none",
+          "description": "Keep normal warning policy, prepare a reviewed report message, or prepare a reviewed message with the residual files attached."
+        },
+        "recipient": {
+          "oneOf": [
+            { "$ref": "#/$defs/recipient" },
+            { "type": "null" }
+          ],
+          "default": null
+        },
+        "subject": {
+          "type": "string",
+          "default": "Unassigned files in campaign {{local:campaign_name}}"
+        },
+        "text": {
+          "type": "string",
+          "default": "The campaign build found {{local:residual_file_count}} file(s) that were not assigned to a recipient.\n\n{{local:residual_file_list}}"
+        }
+      },
+      "additionalProperties": false,
+      "default": { "mode": "none", "recipient": null }
+    },
     "zip_config": {
       "type": "object",
       "properties": {