fix(webapp): correct entitlement cache stale TTL

The stale parameter on @unkey/cache Namespace is the TOTAL ttl,
not an additional window beyond fresh. Setting fresh: 60_000 and
stale: 60_000 gave a fresh-only entry that expired entirely at 60s
with no SWR window. Setting stale: 120_000 yields the intended
behavior: fresh 0-60s, stale-revalidate 60-120s.

Verified locally with agentcrumbs by running through cache miss,
fresh hit, stale revalidate, and stale-with-failed-bg-revalidate
scenarios against a live billing server.

Author: ericallam

apps/webapp/app/services/platform.v3.server.ts

@@ -73,8 +73,8 @@ function initializePlatformCache() {
     }),
     entitlement: new Namespace<ReportUsageResult>(ctx, {
       stores: [memory, redisCacheStore],
-      fresh: 60_000, // 60 seconds
-      stale: 60_000, // 60 seconds
+      fresh: 60_000, // serve without revalidation for 60s
+      stale: 120_000, // total TTL — fresh 0-60s, stale-revalidate 60-120s
     }),
   });