feat(push): owner-only gate and subscription body validation (T10)

isOwner compares the session email to the configured owner; the body
matches the browser PushSubscription.toJSON() shape, reporter resolved
server-side.

server/utils/isOwner.ts

@@ -0,0 +1,7 @@
+// Owner-only gate for Web Push (T10). v1 notifies a single configured owner
+// (DESIGN G3); the owner email comes from runtime config server-side. If no
+// owner is configured, nobody qualifies — push enrolment stays closed.
+export function isOwner(email: string | undefined, ownerEmail: string | undefined): boolean {
+  if (!email || !ownerEmail) return false
+  return email.toLowerCase() === ownerEmail.toLowerCase()
+}