feat(media): add retention metadata to media collection

Adds custom.retention (monthly purge, 90-day post-deletion hard-delete)
to the media Payload collection. No uploadedBy field exists in the
collection so no custom.pii annotation is needed.

packages/media/src/integrations/cms/collections/media.ts

@@ -2,6 +2,16 @@ import type { CollectionConfig } from "payload";
 
 export const media: CollectionConfig = {
   slug: "media",
+  custom: {
+    retention: {
+      purgeSchedule: "monthly",
+      postDeletion: {
+        duration: "P90D",
+        trigger: "after-deletion",
+        action: "hard-delete",
+      },
+    },
+  },
   upload: {
     mimeTypes: ["image/*", "application/pdf"],
   },