fix: CLI improvements for vanilla WAA automation

Key changes:
- Change default emulator IP from 172.30.0.2 to 20.20.20.21 (official WAA)
- Export OPENAI_API_KEY before calling run-local.sh
- Add automatic results download after benchmark completion (--no-download to disable)
- Fix API key passing in both "reuse container" and "fresh start" paths
- Update all internal_ip defaults and CLI argument defaults
- Standalone Dockerfile using vanilla WAA dev mode
- Improved disk space management and auto-cleanup

These fixes enable fully unattended vanilla WAA benchmark runs via:
  uv run python -m openadapt_ml.benchmarks.cli vm run-waa --num-tasks 5

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: abrichr