Gap: infra-as-code / preview environments

**Seen in:** Encore.dev · **Priority:** Medium

Encore provisions matching cloud infra per environment from code-declared dependencies (queues, cron, secrets) and spins up automatic PR preview environments. No equivalent concept here.

Deliberately kept separate from the Deployment Target feature pack (`README.md`): that pack generates static deploy manifests, it does not provision or manage infrastructure.

**Deferred** — large scope jump. Revisit only after the Deployment Target pack ships.

Wait for the Deployment Target feature pack to ship, then start with README.md and compare its static deploy manifests with the requested infrastructure provisioning and PR preview environments. Done means defining and implementing an agreed equivalent concept; this issue provides no files, tests, or narrower entry point yet.

Written by the indexing model from the issue text.