fix(podman): reuse IPv4 primary listener on macOS

[matthewgrossman]

Summary

Remove the stale macOS Podman IPv6 listener split now that the gateway reuses a primary listener that covers the driver callback address. Local Podman workflows return to the standard 127.0.0.1 gateway endpoint.

Related Issue

No issue required: this is a localized correction that removes the workaround introduced in #2622 after primary-listener reuse landed in #2739.

Changes

• Remove the macOS Podman ::1 primary-listener override from the local gateway launcher.
• Exercise the gateway built-in IPv4 loopback default in the Podman E2E harness.
• Remove the IPv6-specific health-probe proxy bypass.
• Preserve driver callback-address discovery so Linux and explicit non-covering binds can still receive a callback-only listener.

Testing

• mise run pre-commit passes
• cargo test -p openshell-server gateway_listener passes (17 tests)
• mise run e2e:podman (running separately in the main task)

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)

[github-actions]

Label test:e2e applied for 3d421eb. Open the existing run and click Re-run all jobs to execute with the label set. The run will execute the standard E2E suite after building the required gateway and supervisor images once. The matching required CI gate status on this PR will flip green automatically once the run finishes.