Revert "feat: keep the sandbox provider step visible when runtime env satisfies it"

[mrubens]

Reverts #403

[roomote-roomote]

3 issues outstanding. See task

• apps/web/src/app/(onboarding)/setup/hooks.ts:421 — The deployment-wide setupSatisfied shortcut can skip configuration for a different selected provider. If one provider is runtime-configured and an unconfigured provider was selected, an unpinned setup re-entry advances without collecting the selected provider's required credentials.
• apps/web/src/trpc/commands/setup-new/index.ts:1629 — An already-configured credential-backed provider choice is recorded without becoming the runtime default, while the restored config-step predicate skips any configSatisfied provider without checking the effective default. An unpinned resumed setup can therefore finish with the new provider selected while tasks still dispatch through the previous provider.
• apps/web/src/app/(onboarding)/setup/StepComputeConfig.tsx:173 — Every hosted-provider confirmation now requires a hosted-ready worker image even when all required managed artifacts already exist. With a locked local-tag DOCKER_WORKER_IMAGE, Continue is disabled although the server can accept the existing artifact and only needs this confirmation to commit the provider default.

_{Reviewed 33c4bb9}