fix(e2b): accept nullable sandbox information domains

[SaladDay]

E2B SDK information responses can omit the sandbox domain. The provider treated these valid responses as ownership failures, rejecting provisioning before bootstrap and preventing cleanup from reaching Kill. Accept the SDK’s nullable information field while retaining metadata, template and resource checks.

Create connection destinations remain strictly validated, and restoring saved connection material validates its destination before any envd request. Information responses never supply connection material.

Validation: 5 template tests, 222 helper tests, the generated helper contract, and Go E2B adapter tests pass. Regressions use the pinned SDK model conversion and cover lifecycle, nullable/omitted domains, foreign destinations, uncertain Create and saved-connection recovery. Negative controls reproduce both the original failure and the unsafe recovery behavior without the guard.

---

^{Need help on this PR? Tag @codesmith-bot with what you need. Autofix is disabled.}