Isolate gate host identity and IPC

[chasebryan]

Summary

• run every copied gate command in private IPC and UTS namespaces
• replace the host name with the fixed orange-gate identity and assert distinct namespace IDs
• assert that fresh System V message, semaphore, and shared-memory tables are empty
• protect the exact namespace contract with policy digests and mutation coverage

Verification

• scripts/ci/check-repository
  • policy 0.2.87
  • 288 Python tests
  • Rust debug and release suites: 162 + 74 + 32 + 9 tests each
  • two relocated optimized builds matched byte-for-byte
  • 7 documentation tests
  • final policy and source-identity checks passed

Residual risk

• local passwordless sudo fallback execution was unavailable because this host requires an interactive sudo password; the preferred unprivileged user-namespace path passed locally, and hosted Required CI will exercise the configured fallback if the runner rejects user namespaces
• the host kernel, namespace implementation, fixed system tools, caller-provided standard descriptors, and non-System-V host identity/IPC surfaces remain trusted or residual boundaries

Rollback

Revert this commit to remove the IPC/UTS namespace flags, fixed hostname setup, namespace-ID assertions, and related policy/docs updates.