fix(cloud): declare local launcher dotenv dependency at its owning boundary

Billing payment replay cannot reach any payment assertions in PR #31694. Both hosted attempts terminate the cloud API launcher before its health port opens. The uploaded .logs/cloud-api.log shows ENOENT while resolving package dotenv from packages/cloud/scripts/admin/local-dev-helpers.ts, followed by sync-api-dev-vars exited with code 1. The outer harness then waits 180 seconds and retries the same failed startup. Chat PR #31699 also reports a failed payment replay job; its server cause is not yet independently checked.

The helper imports dotenv outside the API/shared workspace directories that declare that dependency. Resolve dependency ownership for this root-owned script without widening or weakening payment assertions. Verify the helper resolves from a clean installation and the existing local-stack path boots; repeat the hosted payment replay on the repaired head. Do not raise timeouts or suppress the check.

Evidence: GitHub run35283860192 attempt2 job105458125249, uploaded billing-payment-replay-e2e-2/.logs/cloud-api.log. No credentials or provider calls are required for this loopback stack.