fix(docker): pin validated sandbox host mappings

[raghusubramanyam]

Adds a narrow Docker driver extra_hosts capability for sandbox creation. Literal IP addresses only; reserved gateway aliases and invalid hostnames are rejected. Connect uses it only with a signed private Platform host and one exact policy-admitted IP.\n\nValidation: cargo test -p openshell-driver-docker --lib --no-default-features (101/0).

[github-actions]

This pull request has had no activity for 14 days and is now marked stale. It may be closed in 7 days if there is no further activity.

[agents-lightforge]

[hugo] /ok to test 4c886a1

[agents-lightforge]

/ok to test 4c886a1

[agents-lightforge]

[Forge] Triage, not a code review. This PR and Shell NVIDIA#129 are the same decision taken two opposite ways; exactly one is right.

#12 adds driver_config.extra_hosts to the Docker driver — the exact mechanism Shell's openshell_platform_driver_config used to emit {docker: {extra_hosts: {($host): $ip}}} through --driver-config-json. aegis-connect-shell NVIDIA#129 deletes that producer (bin/aegis-connect-install.sh:2073,2769), replacing it with a validate-only call on the stated rationale that OpenShell's policy DNS resolves a private Platform hostname and allowed_ips enforces the resolved address. If that rationale holds, #12 lands a feature with no caller. If #12 is needed, NVIDIA#129 removed a load-bearing pin and private-Platform installs lose resolution silently. Settle it before either merges.

Targeting: base is main, the upstream-tracking branch. Connect-specific driver changes merged there do not reach lightforge-main and pollute the mirror. Retarget to lightforge-main and rebase — this head is 40 behind it. Note the current green is not transferable: with base=main only 3 check-runs ran here against 12 on #9, so the workflow set differs by base.

[agents-lightforge]

[hugo] Superseded by the reviewed Wave-1 direction in #11. Connect no longer requires caller-controlled Docker extra_hosts; #11 head 0968ba8b removes that surface and rejects it as an unknown field. The unique documentation in this PR describes the removed capability and should not be carried forward.