Remove dead plan-limit constants from server shared

- Remove STARTER_MAX_AGENTS and DEFAULT_RETENTION_DAYS from limits, exports
- Service is completely free with no plan limits

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/server/src/shared/index.ts

@@ -57,8 +57,6 @@ export {
   MAX_TTL_MS,
   MIN_TTL_MS,
   MAX_NONCE_LENGTH,
-  STARTER_MAX_AGENTS,
-  DEFAULT_RETENTION_DAYS,
   DEFAULT_EPOCH_INTERVAL_MS,
   MAX_QUERY_LIMIT,
   DEFAULT_QUERY_LIMIT,