test(campaign): prove GreenMail delivery journey

examples/greenmail-delivery/fixture.json

@@ -0,0 +1,22 @@
+{
+  "scenario": "greenmail-delivery",
+  "campaign_file": "campaign.json",
+  "required_modules": [
+    "core",
+    "access",
+    "audit",
+    "campaigns",
+    "mail"
+  ],
+  "required_capabilities": [
+    "mail.campaign_delivery"
+  ],
+  "transport": "local GreenMail SMTP/IMAP test bed",
+  "credentials": "local environment only; never copied into Campaign JSON or evidence",
+  "expected": {
+    "entries_count": 1,
+    "built_count": 1,
+    "smtp_accepted_count": 1,
+    "imap_appended_count": 1
+  }
+}