refactor: remove molecule_ci_guard — adds complexity, no value

The cross-runner cancellation guard was killing healthy molecule slots
when unhealthy slots failed, defeating fail-fast: false. With fail-fast:
false and no guard, slots on healthy runners complete independently.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

README.md

@@ -226,10 +226,6 @@ python -m devx.molecule.distribute_molecule --runner-index 1 --max-runners 3
 python -m devx.molecule.distribute_molecule --list              # list all scenarios
 python -m devx.molecule.distribute_molecule --list-platforms    # list platforms
 
-# Run molecule tests with cross-runner fail-fast
-python -m devx.molecule.molecule_ci_guard pair1 pair2
-python -m devx.molecule.molecule_ci_guard --roles-root ansible/roles pair1 pair2
-
 # Run all molecule scenarios locally (sequential)
 python -m devx.molecule.molecule_all
 python -m devx.molecule.molecule_all --bin .venv/bin
@@ -303,7 +299,6 @@ devx --version
 | `devx molecule all` | Run all molecule scenarios on all supported platforms |
 | `devx molecule discover-runners` | Discover available Gitea Actions runners |
 | `devx molecule distribute` | Distribute molecule test pairs across parallel runners |
-| `devx molecule guard` | Run molecule tests with CI failure polling |
 
 See [CLI Commands](https://git.oblachno.oblachno.fyi/oblachno-oss/devx/wiki/CLI-Commands)
 in the wiki for full command documentation with examples.