Expire report files after 1 week, maximum for S3

We didn't see this in tests which use disk storage. But AWS S3 has a
maximum of one week for URL expiry.

app/models/report_blob.rb

@@ -2,6 +2,9 @@
 
 # Stores a generated report.
 class ReportBlob < ActiveStorage::Blob
+  # AWS S3 limits URL expiry to one week.
+  LIFETIME = 1.week
+
   def self.create_for_upload_later!(filename)
     # ActiveStorage discourages modifying a blob later but we need a blob
     # before we know anything about the report file. It enables us to use the
@@ -12,7 +15,7 @@ class ReportBlob < ActiveStorage::Blob
       checksum: "0",
       content_type: content_type(filename),
     ).tap do |blob|
-      ActiveStorage::PurgeJob.set(wait: 1.month).perform_later(blob)
+      ActiveStorage::PurgeJob.set(wait: LIFETIME).perform_later(blob)
     end
   end
 
@@ -35,6 +38,6 @@ class ReportBlob < ActiveStorage::Blob
   end
 
   def expiring_service_url
-    url(expires_in: 1.month)
+    url(expires_in: LIFETIME)
   end
 end

config/locales/en.yml

@@ -324,7 +324,7 @@ en:
       subject: "Report ready"
       heading: "Report ready for download"
       intro: |
-        The link below will expire after one month.
+        The link below will expire after one week.
       link_label: "%{name}"
   shipment_mailer:
     shipped_email: