New capability group page docs/capabilities/agents.md consolidating:
- agent_launch_worktree_go_infra
- agent_cleanup_worktree_go_infra
- audit_dod_schema_go_infra (added 'agents' tag to its frontmatter)
3 functions = minimum for a capability group page. Adds row to
docs/capabilities/INDEX.md. End-to-end example shows the launch ->
work -> cleanup -> dod-audit cycle that agent_runner_api (0113)
will orchestrate.
