Add ADR-025 integration-test harness targets to Makefile:
- test-integration HOST=<name> [CERTS=internal|le-staging] [KEEP=1]
- test-integration-clean (prune stale VM snapshots)
Also add tests/integration/.run/ to .gitignore.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>