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. Replace with
direct molecule test execution.

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

docs/tech/ci-cd-workflow.md

@@ -259,9 +259,9 @@ OS platform matrix (defined in `devx.molecule.platforms`), then splits
 the resulting test pairs evenly across the requested number of runners.
 Each pair is encoded as `scenario|platform_name|platform_image|platform_command`.
 
-`devx.molecule.molecule_ci_guard` runs the actual molecule test for a
-given test pair, with CI context (Gitea URL, token, run ID) for
-reporting results back to the commit status API.
+The CI workflow runs each test pair sequentially via a shell loop that
+sets the appropriate `MOLECULE_PLATFORM_*` environment variables and
+invokes `molecule test` directly.
 
 ### Commit Message Validation