ci(e2e): probe VM gateway readiness

[elezar]

Summary

Replace VM gateway readiness checks that depend on the Server listening log
message with active health probes. This keeps VM CI stable when gateway logging
changes and verifies the interfaces the tests actually consume.

Related Issue

No issue. Fixes a brittle CI assumption exposed by #2492.

Changes

• Register the VM E2E gateway before polling and wait for structured
  openshell status output to report a connected gRPC endpoint
• Preserve gateway process-liveness checks and report the last status response
  on timeout
• Poll the configured HTTP health endpoint in the VM orphan-cleanup smoke
  script instead of matching gateway logs
• Update the VM E2E workflow description to document active readiness probing

Testing

• bash -n e2e/rust/e2e-vm.sh tasks/scripts/vm/smoke-orphan-cleanup.sh
• Readiness status matching accepts connected and rejects disconnected
• mise run pre-commit passes
• VM E2E passes in CI

Checklist

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

[github-actions]

Label test:e2e applied for 662fb9b. 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.

[elezar]

gator-agent

Maintainer Approval Needed

Gator validation and PR monitoring are complete.

Validation: This is a small, concentrated CI/E2E robustness fix for VM gateway readiness probing.
Head SHA: 662fb9b286e0a30830885a0c6ff4706b2eb926af

Review: Independent principal-engineer review found no blocking findings.
Docs: Not needed; this changes CI/E2E scripts and does not alter direct user-facing UX or Fern docs surfaces.
Checks: Required gates are green: OpenShell / Branch Checks, OpenShell / Helm Lint, OpenShell / E2E, and OpenShell / GPU E2E.
E2E: test:e2e is applied and OpenShell / E2E passed, including e2e / E2E (rust-vm).

Human maintainer approval is now required.

Next state: gator:approval-needed