Bootstrap runner registration host directory

[cbusillo]

Summary

• Defaults the manual runner registration workflow to a service-user-owned auto root ($HOME/actions-runners) instead of root-owned /opt/actions-runners.
• Bootstraps the official GitHub Actions runner package when config.sh is missing in a new lane directory.
• Starts run.sh after registration so post-registration inventory can observe the lane online.

Live Evidence

The first live apply run proved the control-plane path but failed at host prep:

• Run: https://github.com/cbusillo/launchplane/actions/runs/27157039099
• Plan status: ready
• GitHub registration token fetched and redacted in audit output
• Terminal audit status: failed
• Failure: service user could not create /opt/actions-runners/cm-website-chris-testing
• Post-inventory: still zero runners in cbusillo/odoo-tenant-cm-website

This PR fixes that root-owned directory assumption and the follow-on missing runner package assumption.

Verification

• uv run python -m unittest tests.test_runner_lane_registration
• uv run --extra dev ruff format --check control_plane/workflows/runner_lane_registration_executor.py tests/test_runner_lane_registration.py
• uv run --extra dev ruff check control_plane/workflows/runner_lane_registration_executor.py tests/test_runner_lane_registration.py
• uv run --extra dev mypy control_plane/workflows/runner_lane_registration_executor.py tests/test_runner_lane_registration.py
• git diff --check