An account's apps and checks run with bounded CPU, memory, disk and network, isolated from other tenants #658

A deployed app process and a repository check both run code from the repository. Today they run as child processes of the forge with no resource bound and no isolation beyond the process. Crew agent shells are already sandboxed; app and check execution are not. Open signup needs both bounded and isolated.

Acceptance criteria

• [ ] An app process and a check run under a CPU, memory and disk limit, and are killed cleanly when they exceed it, with that outcome shown.
• [ ] Each runs with the same containment the crew shell has: no read of the forge's data, another tenant's data, or the host; its own writable scratch only.
• [ ] Network egress from an app or check is default-deny with an allow-list, not the forge's full network.
• [ ] Test: from an app and a check on a fresh account's repository, reading the forge's data directory, another tenant's data, and the cluster are all refused, and a process over its memory or CPU limit is stopped.