Integrate Distribution Lists with Campaign recipients

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

@@ -1109,6 +1109,11 @@
           "additionalProperties": true,
           "default": {}
         },
+        "distribution_source": {
+          "type": "object",
+          "description": "Immutable Distribution List recipient, route-decision, and source evidence captured for this Campaign version.",
+          "additionalProperties": true
+        },
         "last_sent": {
           "type": "string",
           "format": "date-time"
@@ -1195,7 +1200,8 @@
             "csv",
             "xlsx",
             "text",
-            "addresses"
+            "addresses",
+            "distribution_list"
           ]
         },
         "source_id": {