add administrator notifications contract

contracts/v1/admin-notifications-response.json

@@ -0,0 +1,18 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "type": "array",
+  "items": {
+    "type": "object",
+    "additionalProperties": false,
+    "required": ["id", "severity", "title", "message", "seen_at", "resolved_at", "created_at"],
+    "properties": {
+      "id": { "type": "string", "format": "uuid" },
+      "severity": { "type": "string", "enum": ["info", "warning", "error"] },
+      "title": { "type": "string" },
+      "message": { "type": "string" },
+      "seen_at": { "type": ["string", "null"], "format": "date-time" },
+      "resolved_at": { "type": ["string", "null"], "format": "date-time" },
+      "created_at": { "type": "string", "format": "date-time" }
+    }
+  }
+}

fixtures/v1/admin-notifications.response.json

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+[
+  {
+    "id": "00000000-0000-0000-0000-000000000001",
+    "severity": "warning",
+    "title": "IP permanently rate-limited",
+    "message": "A source IP reached the login failure limit and requires review.",
+    "seen_at": null,
+    "resolved_at": null,
+    "created_at": "2026-10-25T12:00:00Z"
+  }
+]