style(backend): drop stale "moved/removed" pointer comments

PR #78 review comments 580, 582, 584. Each was a comment
describing what the previous refactor removed or relocated —
information that's in git history, not load-bearing for a
reader of the file as-is.

- claude_bottle/backend/docker/cleanup.py: drop trailing
  "enumerate_active moved to enumerate.py" note.
- tests/unit/test_dashboard_active_agents.py: drop module
  docstring paragraph about which tests moved where.
- tests/unit/test_docker_enumerate_active.py: drop
  "noop-when-docker-missing lives at the cross-backend gate
  now" trailing comment.

607 tests still pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

claude_bottle/backend/docker/cleanup.py

@@ -159,8 +159,3 @@ def cleanup(plan: DockerBottleCleanupPlan) -> None:
             shutil.rmtree(path, ignore_errors=True)
         except OSError as e:
             warn(f"failed to remove {path}: {e}")
-
-
-# `enumerate_active` moved to `backend/docker/enumerate.py` to
-# mirror the smolmachines layout. Cleanup keeps the orphan
-# enumeration; enumeration of live agents is its own concern.