feat(campaign): govern attachment reuse

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

@@ -61,6 +61,16 @@
     }
   ],
   "fields": {
+    "/attachments/reuse_policy/action": {
+      "label": "Duplicate-file action",
+      "control": "select",
+      "description": "Allow and record, warn, require a reasoned review decision, or block repeated use of the same resolved file."
+    },
+    "/attachments/reuse_policy/allow_within": {
+      "label": "Allowed reuse boundary",
+      "control": "select",
+      "description": "Optionally exempt reuse confined to one recipient or one built message."
+    },
     "/attachments/global[]/message_filename_template": {
       "label": "Direct attachment filename",
       "control": "text",