fix: reset createdAt on re-link so linkedAt reflects latest link time

The onConflictDoUpdate block was missing createdAt: now, causing
listForUser/getForUser to expose a stale linkedAt timestamp (mapped
from createdAt) when an environment is re-linked after revoke.

Author: cursoragent

infra/relay/src/environments/EnvironmentLinks.ts

@@ -204,6 +204,7 @@ const make = Effect.gen(function* () {
             managedTunnelsEnabled: request.managedTunnelsEnabled,
             createdByDeviceId: request.deviceId ?? null,
             revokedAt: null,
+            createdAt: now,
             updatedAt: now,
           },
         })